Intermediate temperature reactive dyes have the problem of "unevenness", which is prone to dyeing defects such as color spots, chromatic aberrations, and stains. This is because there are two major defects in the dyeing performance of moderate temperature reactive dyes:
①The stability of salt and alkali solution is poor, and the phenomenon of "aggregation" is easy to occur.
The molecular structure of medium-temperature reactive dyes generally contains 1-2 strong hydrophilic groups -S03Na, and there are also hydrophilic β-hydroxyethyl sulfate reactive groups, so its solubility is good. Most of the neutral softened water at 60°C can reach ≥100g/L.
For example, Reactive Brilliant Blue KN-R and Reactive Turquoise Blue BGFN have a solubility of up to 150 g/L at 60°C and 80°C. However, since reactive dyes can only obtain higher dye uptake in the presence of electrolytes, they must be dyed in a large amount (30-60 g/L) electrolyte dye solution. The presence of electrolyte will significantly reduce the solubility of the dyestuff. Although the aggregation of most dyes in a neutral salt bath (color absorption bath) is not enough to significantly affect the dyeing quality, some dyes with poor salt-solution resistance and stability will cause harm to the dyeing quality. For example, the dye solution of reactive turquoise blue BGFN 15 g/L, the ability to tolerate salt at 60°C is only 80 g/L, that is, if the salt concentration is greater than 80 g/L, the dye will cause significant aggregation or even flocculation, thereby jeopardizing the dyeing quality. .
Especially when the alkali dye solution becomes alkaline, the aggregation tendency of the dye will become greater. The degree of aggregation of many dyes can even reach the point of separation from water in a short time. Commonly used active bright yellow series and active brilliant blue series are typical representatives.