Why is reactive turquoise dip dyeing easy to produce color spots and stains?

When the medium temperature reactive turquoise blue is dip-dyed, the reason why it is easy to produce color spots and stains is because the reactive turquoise blue has the defects of salt resistance and poor alkali dissolution stability.

The medium-temperature active turquoise blue has good salt-dissolution stability under the normal concentration of electrolyte (<80g/L). The degree of agglomeration of the dye is not sufficient to compromise the quality of the dyeing. Under the normal concentration of soda ash (<25g/L), the alkali dissolution stability is good, and the aggregation of dyes is not obvious. However, in the solid solution with salt and alkali coexisting, its dissolution stability will be greatly reduced. After testing, once the mixed concentration of salt and alkali in the fixing bath is greater than 80g/L, the dyes in the dye liquor will not only undergo significant or even serious "flocculation", but also form flocs containing dyes on the surface of the dye liquor. of a lot of bubbles. Once these foams adhere to the fabric, they can cause color spots and dyeing defects.

There are two reasons for the flocculation of active turquoise blue in the fixing bath:

①In the fixation bath, the coexistence of salt and alkali (soda ash is also an electrolyte) greatly increases the concentration of sodium ions (Na+) in the dye liquor. Due to the influence of the same ion effect, the degree of ionization of the hydrophilic groups in the dye is increased. become smaller, resulting in a decrease in the hydrophilicity of the dye.

D-SO3 Na       ←→     D-SO3+Na

Weak hydrophilicity   Strong hydrophilicity

On the other hand, due to the large hydration ability of Na+, it can adsorb a large number of polar water molecules in the form of direct or indirect hydration layer, thereby producing a large salting-out effect on the dissolved dyes.

②In the alkaline bath, the active group of β-hydroxyethylsulfone sulfate in the dye will undergo elimination reaction, and the sulfate group will fall off and become vinylsulfone group. As a result, the original hydrophilic group is changed into a hydrophobic group, and the water solubility of the dye itself is significantly reduced.

The hydrophilicity of the dyes decreases suddenly, the repulsive force against water increases suddenly, and the dyes in the water aggregate with each other in order to obtain stability.