Today Post::Dyestaff Selection in Reactive Dyeing

Dyestuff Selection in Reactive dyeing

The selection of reactive dyestuff for a tri-chromatic or bi-chromatic combination plays a very important role in the performance and reproducibility of reactive dyeing in textile processing. The following points are to be borne in mind, while selecting the dyestuff for a combination shade.
Solubility of individual dyestuff in grams liter without salt (straight) and with salt should be checked prior to dye selection for a combination shade. In a tri-chromatic combination, all the dyes should have almost similar solubility property. The dyestuff that gets affected by the presence of salt would, a) produce tonally different shade, b) produce poor rubbing and wash fast dyeing and c) batch to batch difference in depth and tone would result.
Some important Criteria to be considered while selecting dyestuffs for a tri-chromatic matching

Use of Primary colors:
One should try to use the Basic Colors such as Red, G.Yellow and Blue. The secondary colors should be avoided as far as possible.
The Red’s and Blue’s varies with shade and requirement of fastness properties.
Dyes with similar Exhaustion and Fixation values:
The Reactive dyeing takes place in three steps. viz.,
1. Exhaustion ( primary and secondary)
2. Fixation
3. Wash off
Normally two types of exhaustion take place while dyeing. These are primary and secondary exhaustion.
Primary Exhaustion is the amount of dyestuff migrated on the substrate in the presence of salt. While secondary exhaustion is the total amount of dye migrated on the substrate in the presence of salt and alkali.
While selecting a combination, one has to ensure that the Percentage Exhaustion (PE) and The Percentage Fixation (PF) of dyes should be similar.
In the case of
Reactive ME Dyes PE is 60 to 70%
Reactive HE dyes PE is 70 to 80%
Reactive VS dyes PE is 40 to 50%
If is always preferable to use dyes with PE about 60 to 70%, i.e., ME dyes. Patchy dyeing may occur if peoper care is not taken while using dyes with higher PE, or lower PE.
Dyes With Similar Affinity:
Generally the dyes are classified as Low, Medium, High and Very High affinity dyes.
For Exhaust dyeing, High and very high affinity dyes and preferred. Where as low affinity dyes are used in continuous dyeing.