Source: Technical Service, Atul Ltd (Colors Division), Valsad, Gujarat, India


The Indian Textile Industry, forefounder of nations industrialization, employment generator & revenue earner is experiencing a major upheaval in todays stiff global competition.


The textile processor is caught up in a web of fierce competition from other Asian countries, stringent environmental/ pollution regulations, scarcity of trained man power, escalating energy costs & dwindling export earnings. This has brought in awareness in terms of need for technology upgradation, machinery modernisation, innovative application techniques, cost optimized processing & increasing production capacities for achieving economies of scale. One of the ways to minimize the impact of water, energy, effluent treatment costs, enhancing per person productivity is by resorting to continuous dyeing methods in place of short batch wise processing.


Vat dyes are best suited for such continuous dyeing application by Pad Dry Chemical Pad Steam process, where the thrust is on uniform, level dyeing in long yardages, meeting stringent fastness requirement, lab to bulk reproducibility, minimal tailing (shade grouping) and low effluent discharge. However, there are various factors which determine trouble free application of Vat dyes on continuous dyeing range


Atul is the only Indian dyestuff manufacturer who has successfully stood up for more than 50 years & survived all these upheavals based on its strong R & D, capacity to adopt to market trends & innovative product developments. Atul has developed a new range of micro-disperse Vat dyes- Novatic MD, a full range covering entire shade gamut exclusively suited for dyeing of Cotton & blends in woven fabric form on continuous dyeing range.


A Schematic diagram of continuous dyeing range is given below.



The salient features of Novatic MD dyes are



The salient features of Novatic MD Dyes are:


v      Super-fine micro molecular particle size (below 1 micron)

v      Stable dye dispersion properties

v      Speck-free performance

v      Ready to use non-dusting formulations

v      Non-foaming

v      No obnoxious odour

v      Ease of reduction

v      Perfect solidity of shades

v      Colour constancy under different illuminant systems

v      High migration properties resulting in uniform level dyeing

v      Minimal staining on Polyester

v      High shade build up

v      Optimum thermal Stability under high temp finishing conditions

v      Stability to water spotting and hot pressing

v      Meets stringent quality / fastness demands especially light, repeated washings, laundering & post bleaching.

 

The particle size distribution of the dyestuff plays a vital role for considering suitability of any dyestuff for continuous processing. In Novatic MD range, the individual dye particle size is controlled & the average is kept uniformly below 1 micron, even the standard distribution of dye particle size is strictly monitored so as not to have some dye particles of below 0.1 micron. Some of the problems associated with bigger than average size dye particles are


v    Inferior dye dispersion affecting dispensing system which could block /choke feeding lines

v    Specky dyeing

v    Precipitation /sedimentation in the dye bath resulting in tailing or deposition on padding rolls, etc.


Whereas, very small dye particles are also not beneficial as such fine dye particles tend to agglomerate easily during application process again resulting into above problems. Hence stringent control over particle size distribution is a key to controlled dyeing.


To further ensure & control dispersion stability it is necessary to perform various dispersion stability checks such as


v      Dispersion by Flow test

v      Danriver Filteration test (AATCC 2/4),

v      Separating funnel stability test

v      Speck test & Sandwich cone test.

The Novatic MD dyes have uniform, high shade build up properties & are standardized specifically by continuous dyeing process. The individual dyes also have almost similar shade build-up characteristic to ensure on tone build-up as shown below for some of the most commonly used dyestuffs.


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Novatic MD dyes have optimum migration properties under Pad-Dry-Chemical Pad-Steam application process, which controls centre selvedge, face- back variations, resulting in uniform level dyeing.




 

Additionally some other check points to further control this are


v      Maintaining optimum liquor level in the dye trough

v      Maintaining pad roll hardness between 70 - 80 Shore

v      Maintaining uniform nip pressure across the width

v      Maintaining even dye liquor distribution across the width

v      Maintaining uniform moisture, core pH & temp of ready for dyeing fabric

v      Maintaining uniform temp of chemical pad bath at about 20 deg C

v      Maintaining adequate concentration of Alkali & Reducing agent in the pad bath.


For further details on this new generation, improved technology dye range & for more details on individual dye properties in terms of


v      Particle Size distribution

v      Reduction potential

v      Dispersion characteristic

v      Migration behaviour during drying & steaming

v      Colour constancy

v      Thermal stability under high temp conditions

v      Robustness to dye bath variables & steaming conditions

v      Effect of various post dyeing thermo-chemical finishing conditions, etc.



About the Author:


For further information kindly contact at: dbs@atul.co.in



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