Improving the wet rubbing fastness of reactive dyed deep-colored fabrics is one of the important ways to improve the quality of textiles and overcome the export barriers of textiles.
The main reasons for the poor wet rubbing fastness of textiles are the floating color transfer of water-soluble dyes and the mechanical rubbing transfer of colored nits (10~40μm). The wet rubbing fastness of dyed cloth refers to rubbing the dyed cloth sample with wet white cloth according to the specified conditions, and according to the degree of staining on the white cloth and the standard gray staining sample card to compare and evaluate, that is, the dye molecules and colored fiber particles pass through. The extent to which the interface contact is transferred to the test cloth. Under the same fabric, the same dye, the same pretreatment and dyeing process conditions, the darker the color, the worse the wet rubbing fastness.
The water-soluble group in the reactive dye molecule is beneficial to the dissolution and dyeing of the dye, but it is the main factor that causes the poor wet rubbing fastness of dyed fabrics. Due to the presence of water on wet white cloth, reactive dyes tend to leave the fabric and enter water. Therefore, for the same reactive dye dyeing, the dry rubbing fastness can reach 4~5 grades, and the wet rubbing fastness can reach 2~3 grades.
Measures to improve wet rubbing fastness
1. Select reactive dyes with less floating color after dyeing
Floating color is the main reason for the unqualified wet rubbing fastness of dark-colored fabrics.
Floating dyes of reactive dyes include dyes that have been adsorbed on fibers without reacting with fibers, partially hydrolyzed dyes, and vinylsulfone-based dyes that have eliminated sulfate. The total amount of floating dyes can be expressed by the difference between the final dyeing rate E and the final fixing rate F in the SERF value of the reactive dye dyeing characteristic value, that is, the E-F value.
Therefore, reactive dyes with a small amount of floating color after dyeing must be selected, that is, a dye with a low E-F value, in order to remove the floating color. If the fixation rate is high, the dye will be fixed to the fiber after dyeing, and the amount of floating color can be greatly reduced.
For example, Cibacron C type, F type, Procion H-EXL and other reactive dyes have a color fixing rate higher than 80%, and the amount of floating color after dyeing is relatively small, which is conducive to removing floating color.
However, the final dyeing rate E has a certain relationship with the primary dyeing rate S, so the directivity of reactive dyes cannot be too high. Generally, reactive dyes with a fixation rate F lower than 70% and an E-F value greater than 15% are difficult to remove floating color and are not suitable for dyeing deep and dark colors.
2. Choose reactive dyes with high lifting power
The concentration of dyes used in deep color dyeing is high, and the amount of floating dyes increases. The adsorption of dyes by fibers has a saturation value. Generally, the dye concentration should not exceed 10% of the dyeing saturation value. Excessive dyes cannot be dyed and fixed, and will accumulate on the surface of the fabric, thereby affecting the wet rubbing fastness of dyed products.
For deep and intense colors, reactive dyes with high lifting power must be used.
The multi-reactive group reactive dyes developed in recent years, such as Cibacron deep red S-B, have three times the lifting power of general red reactive dyes (such as CI reactive red 239,195); other three reactive group dyes such as Cibacron red C-2G (CI reactive red 228) has two vinylsulfone groups and one monochloro-s-triazine group, Cibacron Red FN-3G (CI Reactive Red 266) has a monochloro-s-triazine group, one fluoro-s-triazine and one vinylsulfone group each, Remazol Red BS There are two vinylsulfone groups and one monochloro-s-triazine group. They all have excellent high depletion rates, high fixation rates and high lift power, and their hydrolyzed dyes are easy to remove.
3. Reasonable dyeing and finishing process
In addition to the correct selection of dyes, a reasonable dyeing and finishing process can also improve wet rubbing fastness. The smoother the fabric surface, the higher the wet rubbing fastness, so the singeing should be clean, and the colored fiber particles should be reduced at the same time. The gross effect of dyed semi-finished products directly affects the dye penetration during dyeing. Adding penetrating agent and mercerizing treatment is beneficial to improve wet rubbing fastness.
The degree of washout of floating dyes is related to their directness to fibers. The most direct vinylsulfone-based dyes are the most difficult to wash out, followed by hydrolyzed dyes.
The unreacted β-sulfate vinyl sulfone dye has the least directness due to the presence of sulfate water-soluble groups, and is the easiest floating dye to remove. By washing with water and soap, the floating color, electrolyte and alkali agent can be removed. The auxiliaries used in soaping must have good penetrating ability, easy affinity with dyes, and form micelles, reduce the affinity of dyes and fibers, and form inner cores to make dye micelles stably dispersed in water. An auxiliary agent composed of anionic and non-ionic surfactants with penetrating and dispersing functions can be selected, otherwise the effect of thoroughly washing and removing floating color cannot be achieved.
Water quality is a very important factor. If the water hardness is high, the water-soluble groups of the floating dye will form a lake that is insoluble in water, which will seriously affect the removal of the floating dye.
The drying method is also very important. The amount of dye molecule transfer in contact drying is higher than that in non-contact drying.