ADVERTORIAL

Levelling agents: A solution to quality improvementin dyeing

Rakesh Goyal & C N . PrabhuYogeshwar Chemicals Ltd.Copper Roller's Premises,L.B.S Marg, Mumbai- 400078E-mail: yogeshwarchem@vsnl.netWebsite: www.yogeshwarchemicals.com

IntroductionPROCESSING of textiles is a challenging task to meet theexpectations of the customers for the desired appearance,feel and functional characteristics of the end product at thelowest cost with standard quality. Dyeing is a critical opera-tion to produce fabrics with uniform and consistent shadeswith RPT more than 90%. Even a modern process houseequipped with the latest machinery and systems face theproblem of shade variation in the same lot or in betweendifferent lots of the same fabric due to innumerable vari-ables such as fibre substrates, machinery, dyes, auxiliaries,procedures and the skul of the work force.

Selection of dyes and chemicals is as important as ma-chinery used in dyeing.

The levelling characteristics of a dye while dyeing asubstrate is generally governed by• The exhaustion behaviour during initial period of dyeing

and• The levelling out capacity (migration power)

A dye depending on its chemical structure transfers veryslowly on the fibre, tends to dye the fibre uniformly whereasthe dyes which go up rapidly onto the fibre are Mkely to dyeunevenly. If a dye has good migration properties, theunevenness caused during initial phase gets levelled outrapidly under dyeing conditions and a level dyeing is ob-tained. In other words, the levelling capacity of a dye is itsabuity to even out variations in the dye distribution in thesubstrate. In actual practice, the requirements of dyes withmatching compatibility, penetration properties and adequateautomation with minimum supervision cannot be met by allthe processing units and hence a range of levelling agentsfor different dye-fibre systems have been developed by thetextile auxiliary manufacturers to meet the qualiity require-ment.

A range of levelling agents supplied by Yogeshwar Chemi-cals Limited is given in Table 1.

Table 1: YCL range of Levelling Agents

Product Fibre Substrates

Cotton Polyester Wool Acrylic Nylon

Lixatron DKI ^Iixatron ER *Lixatron' VLH ^Iixatrori' DFTLixatron PESLixatron DLEAxcelerator NCEF -Axcelerator NBSI -lixatron NHLixatron BLixatron SETLixatron ANI

y

y

The primary objectives of using levelling agents duringdyeing of different substrates are the following:• To obtain level shades.• Depth and tone of the shade should be the same.• To get optimum colour value.

The levelling capacity depends very much on the charac-teristics of the substrate and dye. The levekiess increaseswith the I increase in temperature, time of dyeing, type andquantity of levelling agent.

The selecdon of levelling agent will depend on the fibresubstrate, class of dyes, type of equipment and the condi-tions of jdyeing used.

Dyes possess different affinities towards texdle material.The affinity to texdle substrate determines the suitabilityand the rate of dyeing. The rate of dyeing can be controlledby altering the dyeing condidons. It is because of the factthat the dyes having a high affinity for the fibre are likely toproduce I uneven dyeings if their rate of dyeing is notretarded.! The rate of dyeing can be controlled by incorpo-rating certain auxiliaries, which either compete with the dye

O NOVEMBER 2009

ADVERTORIAL

for the fibre sites thereby reducing the effective rate ofdyeing or combine with the dye forming a loose complex,which then cannot be absorbed on the fibre surface. Sub-sequently the complex gets broken at higher temperatureand dye is again made available.

I'he mechanism of action of levelling agents used duringdyeing of polyester, cotton, wool and acrylic fibres is de-scribed in this article.

Dyeing of Polyester

With the introduction of texturised polyester yarns andmultifibre blend composition, the dyer is very often facedwith the problem of level dyeing.

Causes for shade variation in polyester fibre are thefollowing:• Different merge numbers.• Denier variation from lot to lot.• Difference in thermal history of yarn.• Variation in yarn specifications and fabric structure.

Disperse dyes are generally classified into three groups asunder:

Low energy dyes : Good migration propertiesMedium energy dyes : Low er niigradon propertiesHigh energy dyes : Limited migration propertiesThere is a compromise between ease of level dyeing on

one hand and fasmess to sublimation on the other.

Migration rating of disperse dyes

The general criteria for giving migration rating to dis-perse dyes based on migration test are given in Table 2.

While produc-ing tertiary shades,dyes having simi-lar migration rat-ings have to beselected. A dyehaving a migrationrating of five lev-els out easily, whilethat with a migrat-ing rating of onehas poor levellingproperties.

The non-ionic levelling agents increase the solubility ofthe disperse dye thereby lowering the initial strike rate andoverall rate of dye uptake.

The carrier type of levelling agents are used in HT/HPdyeing of polyester to get level dyeing. These levellingagents promote migration of the dye with low migrationpower during dyeing. These levelling agents are added to thedye bath only after the maximum dyeing temperature is

Table 2: Migration rating ofdisperse

Dye retained byoriginal dyeing(%)

Up to 5050-5555-6060-6565-7070-7575-80

dyes

Migration rating

5 (Best)4-54 (Good)3-4 (Fair)32-32 (Poor)

reached in order to avoid rushing of the dye during theheating phase.

Lixatron DFT: is a levelling agent for polyester dyeing.It can be used as a stripping agent for disperse dyes whenused in higher dosage.

Lixatron PES: has excellent levelling and dispersingaction during dyeing of polyester with disperse dyes.

Dyeing of cotton with reactive dyes

Lixatron DKI: is an amphoteric surfactant which is alevelling agent for substantive (direct) and reactive dyes oncotton.

Amphoteric surfactants contain both positive and nega-tive charges in the same molecule. A particular ionic chargeunder given conditions will depend on the pH of the bath.Thus, under alkaline conditions the molecules act as anionicspecies whue under acidic conditions they behave as cat-ionic species. At neutral pH i.e. at isolectric point the ioniccharges are balanced and the molecule carries no charge.

This means an amphoteric product is capable of interact-ing with anionic cotton dyes in the dye bath, thus, slowingdown their exhaustion and is capable of absorption ontothe fibre, competing with dye, and thereby equalizing varia-tions in affinity on the fibre.

The addition of salt during reactive dyeing creates anelectrical double layer which hides the electrostatic charge,allowing the dye to approach the fibre. The salt also causesaggregation of the direct or reactive dye that have a higheraffinity for the cellulosic fibres. By adding levelling agent theproportion of monomeric form of the dye is increased ascompared to the aggregated dye. The dye molecules thendiffuse within the accessible amorphous regions of the fibreand get fixed by chemical bonding. This, ultimately resultsin level dyeing.

Dyeing of Acrylic YarnAcrylic fibres contain sulphonate groups attached to the

fibre molecule. These groups ionize and produce sulphonateanions in the fibre structure surrounded by an equal numberof sodium cations to maintain electrical neutrality.

During the dyeing of acrylic fibres with cationic dyesfrom an aqueous medium, the sodium cations are replacedby the dye cations which are then firmly held at the negativesides in the fibre structure. However, the dye cations areabsorbed at the faster rate, leading to uneven dyeing.

The problem of uneven dyeing is overcome by addingcertain cationic products to the dye bath when the cationsof these products also compete with the dye cations for thefibre sites, thereby reducing the effective dye concentrationin the dye bath. As a result the dyeing rate decreases. Hence

COLQURAGE O NOVEMBER 2009 99

ADVERTORIAL

the cationic products are called retarding agents of levellingagents.

However, the cationic product does not remain perma-nently in the fibre. During the later stages of dyeing espe-cially at the higher temperature of dyeing, the retardingagent cations are replaced by the dye cations and maximumcolour yield is obtained.

Retardant levelling supplied by YCL are the following:Lixatron ANI: Retardant for acrylic dyeing

Dyeing of wool and nylon with acid dyes

The acid dye solution produce coloured dye anions andsodium cations. In presence of acid during dyeing proteinfibres, the amino group acquires a positive charge by

protonadon which attract and retain the dye anion. As thereaction is reversible, the salt generated acts as a retardingagent.

Different types of levelling agents are used while dyeingprotein fibres. Anionic levelling agents interact with theionized aniino group of the protein fibre and thus retard itsinteraction with the dye anions. The wetting property inher-ent in these levelling agents promotes colour levelling.

The effect produced by levelling agents of another typeis mainly due to their capacity to react with dye anions andthus slow ¡down their interaction with the fibre. These typesof levellers function only if they do not form precipitatewith the dye.

Some non-ionic levelling agents may be also used duringdyeing as they form unstable compounds with acid dyes. I

No. 1 Product of Japan & NOW No. 1 best seller in INDIA

ECO- Friendly & Non-Formaldehyde, Oeko-Tex Std. Passed,

DYE FKEVG ^GENT" R E A F I X T - 8 C O N C. "

We are offering Special Polymer-based Product Non-Formaldehyde typeDye Fixing Agent for Reactive & Direct Dyes

Highly Cone. Product of JAPAN in Qriginal Tin Packing(Product can be diluted to about 6 - 8 times easily with normal water)

Available For Your Direct Import or Ex-stock from our Importer.Also contact us for your requirement of other Textile Auxiliaries &

Speciality Chemicals of Japan.

-: INDENTING AGENTS :-

DYNATEX INTERNATIONAL101 - Manisha Apartment, Pushtikar Soc. Rd.-4, Jogeshwari (West), Mumbai - 400 102.

, E-Mail: dmjani@dynatex.co.in / mr.jani@gmaii.com; Web: www.dynatex.co.inFax: 022 - 2678 0985; Tei: 022 - 2678 0807

100 COLDURAGE O NOVEMBER 2009

Copyright of Colourage is the property of Colour Publications Pvt, Ltd. and its content may not be copied or

emailed to multiple sites or posted to a listserv without the copyright holder's express written permission.

However, users may print, download, or email articles for individual use.