For reactive dyes, in theory, because the dye and the fiber form a covalent bond, water washing can not easily cause dye desorption, fading and bleeding. Therefore, the color fastness of reactive dyeing products is determined not to be fixed. The amount of dye (hydrolyzed dye and a small amount of unreacted dye). If the hydrolyzed dye is removed by soaping, subsequent washing will appear to fade. The soaping fastness is also related to the bonding stability of the bonding dye, and the broken key dye will also be washed away.
Therefore, the factors that affect the color fastness of soaping are, most importantly, the structure and properties of the dye, followed by the processes of dyeing and post-treatment. The reactive dye has a high fixation rate, or a slow hydrolysis rate, a small amount of hydrolyzed dye, and a small amount of dye to be washed and removed. The unfixed dye and the hydrolyzed dye have low directness, good water solubility, are not easily stained, and are easy to wash off. When the dye concentration is high and the amount of residual dye is large, it is not easy to wash off.