RFT PRINCIPLES

Right first time dyeing

R.Monica,' G.Myvizhirajeswari^ & M.Senthil Kumar*Department of Textile TechnologyPSG College of Technology, Coimbatote - 4

ABSTRACT

In dyehouses "Right First Time Dyeing" had been a proven boon to Textile chemical processing industry. It helpslo eliminate extra expense on re-dyeing, re-shading and reproducing the color. This paper deals with dye selectioncriteria, process involved while dyeing, assigning dye uptake, machineries developed, type and principles ofreactive dyeing and benefits involved in right first time dyeing.

In dyehouses processing, cellulosic fibers with reactive dyes, much progress has been made in the quest for zerodefect production by the innovative introduction of controlled coloration technique that has supported thedyeing performance.

Exhaust dyeing using reactive dyes quantify dye migration properties, the degree of process control to achieveshade reproducibility and level dyeing performance. The concept of Reactive Dye compatibility Matrix (RCM)will allow to identify dyes with similar properties and used in combination to support right first time production.It can also be used as a diagnostic tool when optimizing application techniques.

Hence this becomes an important factor for industries to produce a value added product at a higher profit so thatboth the manufacturers and consumers are satisfied.

IntroductionTO improve the financial performance i.e. to increase profitmargin by decreasing the working capital and to withstandintemadonal competitiveness one has to focuss attention onthe need for right first time production. This demands theelimination of wastes at all stages of the textile productionchain. The trends thus are towards lower ratios to increaseproductivity throi^gh reduced fillings draining, heating andcooling fibres and to reduce chemicals. The Reactive dyecompatibility (RCM) can be used to achieve this. Under-standing RCM will allow dyes with similar properties to beidentified and used in combination to support tight firsttime production. Dye selection criteria are based on accurateand consistent standardisation of dyes is the principal re-quirement for optimized dye house efficiency &c right firsttime production. • ,

Exhaust dyeing of cellulose with reactive dyes is a com-plex process. It involves the exhaustion of dye onto the

* Part of B.Tech Textile Technology Under the Guidance ofMr. M.Senthil Kumar (Lecturer)

' B.Tech final student (E-mail id: myvizhL1987@yahoo.co.in)^ B.Tech final student' Lecturer, Dept of Textile Technology

fibre in the presence of electrolyte and then the addition ofalkali to promote the chemical reaction between dye &cellulose. During the "Right First Time" production in theexhaust application of reactive dyes to cellulose the follow-ing will affect the dye regularity.• Hardness in the dye bath ' i M• Bicarbonate in the dye bath

Dye selection criteria

Accurate and consistent standardization of dyes is theprincipal requirement for optimized dye house efficiencyand right-first-time production. A Statistical analysis whichassesses the effect of dye standardization liniits on right-first-time production is shown in Fig. 1 <& 2.

The external factors which influence the process havebeen identified and segregated into two variables.• The Assignable variables - e.g. internal fabric pH at the

start'of the dyeing cfdt, the liquor ratio, the temperaturegradient, the fixation temperature, the electrolyteconcentration, the addition profiles of dye, electrolyteand fixation alkali, the fixation pH and time.

• The random variables - e.g. the impurities in cotton, watersupply, chemicals, and the dyes selected to reproduce thetarget shade.

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RFT PRINCIPLES

100

wo-

OT «

I 1 -T r2£\ *hi.Qy- »/-TAX tl-1t>

STAMDAROISING UMfTS

Fig. 1: Effect of dye standardization onProbability of right-first-timc production.

PROCIOH K-XZX.

VZKK (» in)

Fig. 2: S.E.F. profile.

Process involved in "Right first time dyeing*'

Right first dyeing involves exhaust dyeing using reactivedyes.

Exhaust dyeing of cellulose with reactive dyes is a com-plex process. It involves the exhaustion of the dye onto thefiber in the presence of electrolyte and then the addition ofalkali to promote the chetnical reaction between the dye andcellulose.

The controlled coloration approach has proven to be thebasis of a systematic, structured and successful approach toimprove the right-first time production rate. The leveldyeing performance of reactive dyes has benefited from theintroduction of controlled coloration and it is now per-ceived that shade reprodudbüity is the major obstaclepreventing zero defect production.

Portion wise salt process

The established application profile for reactive dyes isbased on the portion wise addition of electrolyte andfixation alkali. It was developed for application at longliquor ratios and for dyeing equipment such as winches andside paddle machines which have low liquor to fiber inter-change. The low liquor to fiber interchange on these typesof machines demands controlled rates of dye exhaustionand fixation to achieve level dyeing performance. In anattempt to control the rate of dye exhaustion, the electrolyteis added in discrete portions, allowing time for the dye bathto reach equilibrium between the additions. The additionprofiles used to retard the exhaustion of the dye range fromtwo or three equal portions made at the starting tempera-ture to complex pyramid addition profiles often made atdifferent temperatures on the temperature gradient. Onreaching the fixation temperature a period for dye migrationis followed by the addition of fixation alkali. This is gener-ally made in two or three portions, again allowing time for

I

the dye bath to reach equi-librium between additions.The dyeing process is com-pleted by the dye fixationstage. The process is long,complex, labor-intensive, ex-tremely difficult to controland reproduce, and there-fore requires a highly skilledand reliable workforce. Thecomplexity of the process isthe source of many of thelevel dyeing and shade re-producibility problems asso-ciated with reactive dyes.Furthermore, the processdoes not exploit the proper-

ties of more recently developed reactive dyes especiallywhen applied on more modem jet or overflow machines.Table V shows the RCM for dyes applied by the portionwise salt process.

Portion wise Salt vs. Standard process

Comparison of Tables N and V shows that the MJ andLDF values of dyes when applied in a portion wise saltprocess are not optimized and therefore the process re-quires precise control to support level dyeing performanceand shade reproducibility. The standard is a short, simple-process based on a salt-at- start profile and linear additionof fixation alkali.

This process is suitable for medium to heavy shades dyedon unmercerized cotton and does not require exponentialmicroprocessor control of the addition of dyes or chemicals.However, if total automation of machine is available thenthe isothermal method can be used for these shades andsubstrates. '

Isothermal Process '

The isodiermal process offers further improvements inproductivity but because the MI and LDF values in thisprocess are lower than in the standard process more precisecontrol of the dye addition is required.

Assigning the dye uptakeThe performance of a reactive dye is defined by the

S.E.F. profile. The substantivity equilibrium S. representsthe primary exhaustion of the dye in the presence of neutralelectrolyte. The exhaustion equilibrium, E. represents thefinal exhaustion of the dye which takes place after theaddition of the fixation alkali. The fixation value, F, repre-sents the fixation level for the dye. The secondary exhaus-

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RFT PRINCIPLES

don, represented by E-S, takes place simultaneously withdye fixation after the addition of the fixation alkali.

Dyes with a wide range of S.E.F. profiles can be oh-i;iined. Dyes with S values as high as 96% and as low as/7% are commercially available. Dyes with such wjde differ-ences in substantivity will exhibit different levels of perfor-mance and sensitivity to external influences. Dyes with lowsubstantivity will generally be n:iore sensitive to variations inlitjuor ratio and electrolyte concentration. In contrast, dyeswith high substantivity will be robust and provide shadestability to these variations in processing conditions.

During the initial phase of the process, the neutralprimary exhaustion of the dye in the presence of electrolyte,migration and diffusion can take place. Dye which hasexhausted onto the fiber is available for migration, andleveling will take place by the classical mechanism. Theactual migration which takes place during primary exhaus-tion will depend on the cheaiistry of dye - its molecularstructure, physical chemistry and stereochemistry, and onexternal factors-concentration of the dye added to the dyebath, time, temperature, liquor ratio, rate of liquor circula-tion and fabric construction, or in the case of yam dyeing,package format. From practical considerations it is thechemistry of the dye which has the dominant influence onmigration properties and therefore on its level dyeing per-formance.

The migration properties of dyes are easily measuredusing a simple laboratory test. Using color measurementtechniques to measure the depth of shade of the testsamples D2 and B2 it is possible to calculate a migrationindex, MI. as in Equation 1.

Migration Index (MI) = Strength B2*100 / Strength D2

The migration index defines the migration properties ofan individual dye applied by a defined process. A dye withitieal migration properties in a defined process will possessa M7 of 100.

Probably the most critical stage of the reactive dyeingprocess is the addition of the fixation alkali. It is especiallycritical for dyes with a h i ^ ¡ES value. For these dyes, theaddition of alkali increases the substantivity of the dye andexhaustion and rapid fixation take place simultaneously. Therate of fixation must be controlled by the use of complexand time-consuming addition profiles. This requires the useof metering systems to achieve linear fixation of the dyewhich is necessary to secure level dyeing performance.

The migration which can take place dxiring the secondaryexhaustion phase of the process is severely restricted due tothe rapid fixation of the dye and will not significantlycontribute to level dyeing performance. Thus for a dye witha high secondary exhaustion the only control option avail-able to obtain level dyeing is the precise control of the rateof fixation of the dye.

The level dyeing performance of reactive dyes and thedegree of control required to achieve level dyeing aregoverned by the substantivity equilibrium value, the migra-tion which takes place during the primary exhaustion andthe secondary exhaustion which takes place after the addi-tion of the fixation alkali. It is possible to quantify therelationship between these parameters, assign a measure ofdye performance, and define the degree of control requiredto achieve reproducible level dyeing, and robust to smallexpected variations in processing conditions by calculatingan empirical value, the Level Dyeing Factor, LDF, which isdefined in Equation.

Level Dyeing Factor, IJ3F=S/E*MI%

While LDF values are derived from an empirical equa-tion, the values are consistent with expetience and expecta-tions of the performance of dyes which are commerciallyavailable. As with the migration indices, WF values reflectthe performance of individual dyes applied by a definedprocess.

TabU shows the S, E, MI and WF values for the series ofblue dyes previously discussed.

Generally, the LDF value will define the most suitable

Table II:

Dyebaths Based onC.I. Reactive

Blue 171Prodon Navy H-EXLBlue 184Blue 222Blue 225Blue 238

Level

%S

877366454239

Dyeing

VoE

959090889697

Factor

%MI%

609081749189

%LDF

557367374036

CDLOURAGE O DECEMBER 2009

application technique for the dye which will minimize therisk of unlevel dyeing and optimize shade reproducibility.Dyes with high substantivity, low secondary exhaustion, lowMI values and therefore modest LDF values will requirecontrolled addition of the electrolyte after the addition ofthe dyes. In contrast, dyes with low substantivity, highsecondary exhaustion, and medium to high MI values willpossess low LDF values. These dyes will require precisecontrol of the liquor ratio, the concentration of electrolyte,and the addition profile of the fixation «ikaD.

S, Ml and LDF values provide data on the sensitivity ofthe dye to external factors such as variations in liquor ratioand chemical concentrations, but to assess the sensitivity ofthe dye to variations in fixation time and temperature it isnecessary to study the reactivity of the dye. A convenientmethod of assessing the reactivity of the dye is to measurethe time taken for half of the dye to teact, TSO. Table UIshows the variation in T50 values for a range of blue dyesapplied by the manufacturers' standard recommendations.

"«1

RFT PRINCIPLES

Table III: Time of Half Fixation, T50 Minutes

Dyebathg Based onC.I. Reactive

Blue 171Procion Navy H-EXLBlue 184Blue 221Blue 225Blue 238

Alkali

Na^CO,NaOHNa^CO,Na^CO,Na^CO,

Addition profile

linear over 10 min.Linear over 10 min.70% progression over 303 equal adds over 20 min70% progression over 3070% progression over 45

T50

min.

min.min.

(min)

6.011.010.03.03.5

14.0

Machinery DevelopmentsMachine Volume and Liquor Ratio

Tlie volume of an exhaust dyeing machine (Jet,Winch, Circulating >X%ich, Package, and Hank) is avitally important parameter of any exhaust dyeingprocess.

It determines the liquor - to - goods ratio of thedyeing.

Let us think for a moment about the volume of

Lc\elI)evice ICulibruU-d

Viilumr

Walcr Supjih

Fig: Exhaust Dyeing Machine beforeLoading with Fabric.

For this series of dyes the T50 val-ues vary from 3-14 minutes. Fordyes with T5Q values of three min-utes the initial rate of fixation israpid and the addition profile usedbecomes the critical step to effectlevel dyeing performance.

In piece dyeing the target ropecirculation time for cotton knits isnormally two to three minutes. Un-der these circumstances and in ex-treme cases, 50% of dye fixationtakes place before two rope revolu-tions and the addition of fixationalkali is completed. In package dye-ing, the in-outlet-in directional flowqrde is generally set at 10 minutes;e.g., 3-4 minutes in-out and 6-7

minutes out-in. Again, in extreme cases, SOVo of dye fixadontakes place before the in-out cycle and the addition offixadon alkali is completed. Such rapid fixation can only putlevel dyeing performance at risk and therefore precise con-trol is required at this stage of the process. T50 values willdepend on the reactivity of the dye, fixation temperature,and the fixation alkali addidon profile. To support leveldyeing performance the target TSO value should be set at aminimum of ten minutes, or, in piece dyeing five roperevolutions, or in package dyeing one complete in-out/out-in cycle.

The criteria for the selection of reactive dyes, which will,when applied using the principles of controlled coloration,maximÍ2e right-first-time production are based on S, MI,LDF, and T5Q values.' These parameters are the key mea-sures of performance for a reactive dye and represent theRCM. Right-fixst-time production will be maximized withinthe RCM set at:

Lcvd Dcvke

Calibrated

Fig: Exhaust Dyeing Machine withPrepared (absorbent) Cellulose.

Substantivity in neutral electrolyte

Migration Index

LDF

T50

70-80%

>go%

>70%

10 minutes minimum

an exhaust dyeing machine a litde more closely.The machine has a calibrated levelling device (usually at

the side of the machine).The machine is calibrated by the machinery manufacturer

before delivery.Known volumes of water are pumped through a mea-

suring meter (Electro Magnetic Flow meter) which tells usexacdy how much water has been delivered to the ma-chine.

Each water fill level registers on the levelling device, andis therefore calibrated against the known delivered volume.

In this sense, the machine volume before addition ofsubstrate is known, and known quite precisely what is notquite so certain is the "Working Volume" of the machine inthe presence of an absorbent substrate.

Cellulose, and especially knitted cotton, absorbs water,Therefore, the working volume cannot possibly be equalto the calibrated volume. Furthermore, the amount ofwater absorbed (and therefore the difference betweenworking and calibrated volumes) is extremely difficult topredict. It is even difficult to predict for a verticalorganisation. It is well nigh impossible for the commissiondye house.

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RFT PRINCIPLES

Basic principles ofreactive dyeing

Reactive Dyes

Reactive dyes receive their namebecause they contain reactive groupsthat can react with the fiber beingdyed to produce a permanent chemi-cal bond between the dye and thefiber.

There are many different reactivesystems, but the two major reactivegroups, which give their name tothe dye type> a.re"monochlorotriazine" (MCT) dyesand "vinyl sulphone" (VS) dyes.These dyes "react" in different waysand they require different dyeingconditions, particularly in terms ofpH, and temperature and time pro-files.

Dyes can contain more than oneof these reactive groups. If theycontain two of the same group theyare called "homo bifunctional" re-active dyes (e.g. MCT-MCT or VS-VS). With these, each dye moleculeprovides twice as many chances forthe dye to react with the fiber. If a reactive dye contains amixture of two reactive groups it is called a "mixed bifunc-tional" or a "hetero bifunctional" dye (e.g. MCT-VS). Heterobifunctional dyes can normally react under a wider range ofdyeing conditions.

Reactive dyes must be used under the correct conditionsto ensure high fixation levels and better "right first time"dyeing.

Monochlorotriazine dyesTypical dyeing conditions:

• Dye at 80°C• In the presence of an electrolyte (e.g. NaQ)• pH 10.5 after addition of a suitable alkali• Dye for 30-60 mins after the addition of alkali depending

on the depth of fabdc shade

Vinyl sulphone dyes

Typical dyeing conditions:

. Dye at 6O'*C• In the presence of an electrolyte (e.g. NaQ)• pH 11.5 after addition of suitable alkali

Fig: winch Dyeing Machine

Dye for 30-60 mins after the addition of alkali dependingon the depth of shade.

Mixed bifunctional dyes:Monochlorotriazine

Sulphone &

Typical dyeing conditions:

• Dye at 60°C and raise to 80°C to ensure both reactivegroups are used

• In the presence of an electrolyte (e.g. NaCl)• pH 11.5 after addition of suitable alkali• Dye for 30-45 mins at 6O'*C after the addition of alkali

and then ramp to 80°C and hold for 30-60 mins dependingon the depth of shadeThe commercial names of many dyes provide informa-

tion on which reactive group they contain.

Electrolyte

This has long been known as a significant source oftemporary hardness, which can exceed even that of thehardest of incoming water suppUes (see Tabie).

Common salt (NaCl) is sourced from underground de-posits or by evaporation of sea water. In the latter case,

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RFT PRINCIPLES

Total Metal Content

Source

UnpuriGed Rock SaltSource 1Unpurified Rock S^tSource 2Unpurified Sea Salt

Purified Sea SaltPure Vacuum Dried

AU figures are in ppm

Table:by Source

Ca**

1600

22001300

10023

of Common

920

1800260

502

Salt

Fe ***

25

10045

22

calcium and magnesium impurity from discarded sea shellsand mineral salts is highly likely.

Testing prepared cotton for residualchemicals

For any cotton in an aqueous medium there are threephases which we need to concern ourselves with:• The aqueous bath• The surface layer• The internal BATH.

Most testing regimes which screen for the efficiency ofpreparation focus upon the concentration of chemicals inlast aqueous rinse before dyeing.

There are three chemicals which can interfere with suc-cessful dyeing with reactive dyes if carried forward frompreparation into the dye bath:• peroxide (some dyestuff chromophores are extremely

sensitive to peroxide)• Hardness {all dyes susceptible to one degree or another)• Alkali (which will cause premature fixation before

migration and premature hydrolysis before exhaustion andfixation).Once a prepared substrate is placed in an aqueous dye

bath, the temperature will be raised to a minimum of 60 'C.Therefore, anything which is in the interior of the preparedcotton can desorb into the bath.

So - it is the Internal condition of the prepared cotton

Test the prepared fibre here

Fig: Internal Bath of Cotton.

which should be of prime concern.Fortunately, it is relatively easy to ensure that it is the

interior of the fibre which is tested, and not simply thesurface condition.

This can be achieved by extraction of the preparedcotton in boiling distilled water (at the same liquor to goodsratio as that used in dyeing).

The extract can be cooled to room temperature, and thenmeasured for. pH• peroxide• Hardness.

RFT dyeing: Varioud technologies

Luft-roto plus: Economical exhaust dyeingtechnology

The Luft-roto plus and selected Levafix, Remazol andProdon reactive dyes can reduce exhaust dyeing cycles forcdlulosics by up to 30% and virtually reduce water andchemical requirements to one-half. This technology wasdeveloped in cooperation with Thies.

Innodye/InnoVat: New jet dyeing concept

Innodye/InnoVat is a fiexible and economical new jetdyeing technology. Developed in conjunction with Brazzoli,this economical system allows rapid and efficient dyeingwith Levafix, Prodon and Remazol reactive dyes andIndanthren vat dyes. This technology, therefore, meetsdemands for increased fiexibüity and improved color fast-ness. The concept comprises the Innodye dyeing unit andthe InnoVat dyeing process developed spedfically for thisunit. The Innodye unit uses unique vacuum tedmology thatopens up completely new process options. It indudes apatented traversing mechanism with a movable materialbasket. Innodye/InnoVat therefore ensures level dyeingeven on problematic substrates.

Econtrol: Economical new continuous dyeingprocess

Econtrol is a rapid and reliable method of dyeing a widerange of substrates. It does not require steaming or curingand ensures high reproducibility and excellent fixation.Econtrol is a registered trademark of DyStar. It was devel-oped in conjunction with Minford's and is based on theThermo hot flue technology. Econtrol is environment-friendly and dyeing can be carried out without silicate, ureaand salt, thus reducing redpe costs and effiuent load.Econtrol is easy to use in the lab and lab-to-bulk reproduc-ibility is very good. Excellent reprodudbility and high fast-ness levels can be obtained on both lightweight and heavy-

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RFT PRINCIPLES

weight cotton, viscose and Lyocell qualities with selectedLevafix and Remazol reactive dyes.

Fluidyer Reliable dyeing of carpets & pile

Fluidyer technology from Küsters and quality dyes frotnDyStar help dye houses achieve their aims faster, moreeconomically and more reliably. Unlike conventional tech-nology, the Fluidyer applies the liquor direcdy to the fabricthrough rows of holes, giving liquor pick-ups of 80-350%.A joint development project by DyStar and Küsters hasdeveloped this technology for dyeing pile fabrics. Theworld's only Fluidyer pilot plant, located in the servicelaboratory at DyStar's new headquarters in Frankfurt amMain, Germany, is available for test dyeing for customers.

Electrochemical decolonization of textile effluent

The decolonization of effluent is a new technology,which does not require chemicals or the disposal of resi-dues. Electrochemical decolonÍ2ation is based on the prin-ciple that electrons in an electric current split textile dyesinto smaller, colorless parts that are more readily biodegrad-able. A cooperation agreement has been concluded withBentiinger on the marketing of this environment-fdendlytechnology. Pilot trials show that this technology can re-move over 80% of color from dye house effluent, especiallyeffluent contaminated with reactive dyes. It is particularlyeffective for treating effluent from continuous dyeing whichcontains high dye concentrations.

Conclusion

So it is dear that using "Rigjit First Time Dyeing"conceptsprovides broad scope of increasing the profit byreducing the after treatments. This is clear by the followingflow chart

In this competitive world "Only the fittest will survive".The Indian textile industry must improve its Productivity,and particularly in the Dyeing & Finishing sector; and musttarget the Value-Added sectors. This can be achieved mainlyby introducing innovative ideas and applying chemistry to

1

i OmiperlUw

: to fill iln ¡ob Ji t

decrease the production cost and give more quality productsso that the profit margin is increased. Also this type ofdyeing is ecofriendly.

References

• www.dyehouses.com• www.alternative.pdf• CoUishaw, P. S.B. Glover and M. J. Bradbury, Joumai of

die Sodety of Dyers and Colorùts. Vol. 108, No. 1. January1992. pi 3.

• Farrington, D.W. Journal of the Sodety of DiversionColorisU. VaL 105.

. No. 9 September 1989, p301.• Diggle. P., Textile Institute Conference Proceedings,

Ghent, Belgium. 1991.• Glover, B., journal of the Sodety of Dyers and Cokrisis,

Val. 107, No. 5/6. May/June 1991, pi 84.• Carbonell. J., American Dyestuff Reporter, Vol. 76 N0.3.

March 1987, p34.. Bradbury, M. J. P. S. CoUishaw and D. A. S.Phillips, 16th

IFATCC Congress. 1993.. CoUishaw. P. S. D. T. Parkes. I5th IFATCC Congress.

1990.• Lidyard. A. M.. A. Woodcock and P. Noone. journal of

the Sodety of Dyers and Colorists. Vol. 108, No. U.November 1992. p501. •

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