Buyers Guide to Dyes

In today's competitive world, reliable, cost-effective products and latest technological solutions are essential for survival. A lot of factors go in making the dyeing process the right one that not only saves capital for the dyer but also takes care of the environmental problems associated with dyeing as well.

Listed below are some of the parameters and questions that a dye manager must consider before opting for any dyeing process.

Is the process compatible with all the dyes he has opted for
If the process is exactly compatible with the machine with respect to temperature, pH, and material construction and that there is adequate control of these necessary parameters.
The chosen dye gives all the fastness requirements as specified.
Correct dye bath is choosen or not.

'Right first time' is a decisive term in dyeing process. It refers in getting the right shade of fabric the first time without the uncalled for need to re-shade or washing off to reduce the depth of shade. It has many advantages:

Reduction in pollution because of less dye in the effluent
Considerable savings in terms of energy, labour and reprocessing costs
Increased productivity as there is no question of re-processing, so adequate time to dye more production

Dyer encounters a lot of problems while as he takes on the dyeing process. Here in this page a few of such common dyeing problems as faced by the dyer is discussed along with solutions.

Common Dyeing Problems	Solutions
Unstable dye dispersion	Select dyes that has better dispersion stability Application of efficient dispersants
Incorrect dyeing program	The answer lies in optimization of dyeing process. Which means adjustment of the process parameters in a manner so that the entire operation takes place in the shortest possible time. It should not exceed the tolerance limits with respect to reproducibility and levelness. This effectively means quick heating in the temperature ranges where the dye exhausts slowly or is already exhausted. Controlled heating as the dye starts showing a particularly high rate of exhaustion.
Poor light fastness Causes are: Traces of carrier residues on fabric Staining of adjacent fibre Catalytic fading because of unsuitable dye combination	Repeat thermofixation (at high temperature) Selection of appropriate dyes Adjustment of dye selection
Pale areas found after dyeing is over	Proper ventilation of vapours and gases Avoidance of contact with dangerous substances
Deviations in shades of dyeing causes can be- Sensitivity of dyes to hydrolysis, reduction, electrolyte Sensitivity of dyes to metal ions in the dyebath	Selection of dyes very carefully, exact control of pH Giving attention to stability of dye with respect to electrolytes
Presence of Precipitates in the dyebath Causes can include crystallization of dyes due to changes in temperature in the dyebath Usage of volatile carriers	Using systems that has perfect liquor circulation Selection of suitable carriers, usage of overhead heating in the machine
Poor dye fixation	This has been a common problem particularly with reactive dyeing when it comes to batch dyeing of cellulose fibres. This can be taken care of by the use of sophisticated molecular engineering techniques. Use of Bifunctional and low-salt reactive dyes can attain more than 95% fixation rate even for cellulosic fibres. Application of hot rinsing methods
System losses in continuous dyeing processes	Carrying out of the impregnation step in a nip The capacity of the dip trough to be minimized. Separate streams in dispensing the dyestuff and auxiliaries

What exactly is 'Right First Time' Dyeing?

Common Dyeing Problems