The structure of reactive dye molecules can affect wet rubbing fastness

1. Water solubility of dyes

The more water-soluble groups contained on the reactive dye molecule, the more favorable it is for the dissolution and uptake of the dye during the dyeing process, and of course the washing of floating colors. But after the dyeing is completed, the "excellent water-soluble group" becomes an unfavorable factor for wet rubbing fastness. This is because the presence of water-soluble groups will strengthen the tendency of dye molecules to break away from cellulose and dissolve in water. The better the water solubility, the easier it is for the dye to be disconnected from the fiber. In order to solve this contradiction, after the dyeing is completed, the water-soluble group can be blocked by a fixing agent to improve the wet rubbing fastness of the dyed fabric.

2. Directness of dyes

The directness of reactive dyes is mainly related to the molecular weight of the dye, the polarity, the regularity of the structure, the active group and its position. The larger the molecular weight, the stronger the polarity, and the better the regularity of the structure and form, the higher the directness of the dye molecule, and the worse the diffusion performance. The easier it is for the dye to accumulate on the surface of the fabric and not diffuse and transfer into the fiber. Cause too much floating. If the directness is too low, it will affect the fixation rate. Therefore, the directness of reactive dyes is better. The degree of directness can be measured from the Rf value and the penetration test.

3. Active base

The active groups are different, and the covalent bond stability formed by the reaction with the fiber is also different. Generally, the higher the reactive activity of the active group, the worse the stability after bonding. The active group is different, and the covalent bond formed by the reaction with the fiber is different in acid and alkali resistance. The ester bond formed by the reaction of X-type s-triazine reactive dyes with fibers has poor acid resistance and stability. When exposed to acid gas and moisture, the bond between the dye and fiber is likely to be broken; KN-type vinylsulfone dyes react with fibers to ether The bond is more stable against acid hydrolysis, but it is easy to cause the covalent bond between the dye and the fiber to break in the alkaline medium. The M and ME reactive dyes with double reactive groups have higher acid and alkali resistance and stability, but the pH value of the fabric should be kept neutral. Therefore, controlling the pH value of the fabric surface of the finished color cloth is also very important for the wet rubbing fastness of the fabric.