Foreword
Improving the wet rubbing fastness of deep-colored fabrics with reactive dyes is one of the important ways to improve the quality of textiles and overcome textile export barriers.
The main reasons for the poor wet rubbing fastness of textiles are the floating color transfer of water-soluble dyes and the mechanical friction transfer of colored fiber particles (10~40μm). The wet rubbing fastness of dyed cloth refers to rubbing a wet white cloth with a dyed cloth sample according to specified conditions, and comparing the staining degree on the white cloth with the standard gray staining sample card for evaluation, that is, the dye molecules and colored fiber particles pass through The extent to which interface contact transfers to the test white cloth. Under the same fabric, same dye, same pre-treatment and dyeing process conditions, the darker the color, the worse the wet rubbing fastness.
The water-soluble groups in the reactive dye molecules are beneficial to dye dissolution and dyeing, but they are the main factor causing 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 the water. Therefore, for the same reactive dye dyeing, the dry rubbing fastness can reach level 4 to 5, but it is difficult to reach the wet rubbing fastness to level 2 to 3.
Measures to improve the wet rubbing fastness
1. Choose reactive dyes with less floating color after dyeing
Floating color is the main reason for the unqualified wet rubbing fastness of dark and dense colored fabrics.
Floating dyes of reactive dyes include dyes that have been adsorbed on the fiber without reacting with the fiber, partially hydrolyzed dyes, and vinyl sulfone-based dyes that have eliminated sulfate esters. The total amount of floating dyes can be expressed by the difference between the final dye uptake rate E and the final fixation rate F in the SERF value of the reactive dye dyeing characteristic value, that is, the E-F value.
Therefore, it is necessary to choose reactive dyes with less floating color after dyeing, that is, dyes with low E-F value, so as to facilitate the removal of 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 fixation rate higher than 80%, and the amount of floating color after dyeing is relatively small, which is beneficial to removing floating color. Editor: There are no boundaries for dyers, but there is a certain relationship between the final dye uptake rate E and the primary dye uptake rate S, so the directness of reactive dyes cannot be too high. Generally, reactive dyes with a fixation rate F less than 70% and an E-F value greater than 15% have floating colors that are difficult to remove and are not suitable for dyeing deep and dense colors.
2. Choose reactive dyes with high lifting power
The dye concentration used in deep and dense color dyeing is high, and the amount of floating dyes increases. The fiber’s adsorption of dyes has a saturation value. The dye concentration should generally not exceed 10% of the dyeing saturation value. Excess dye cannot be dyed and fixed, and will accumulate on the surface of the fabric, thus affecting the wet rubbing fastness of the dye.
Dyeing deep and dense colors must use reactive dyes with high lifting power.
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 vinyl sulfone groups and one chloro-s-triazine group. Cibacron Red FN-3G (CI Reactive Red 266) has one chloro-s-triazine group, one fluoro-s-triazine group and one vinyl sulfone group. Remazol Red BS has two vinyl sulfone groups and one chloro-s-triazine group. They all have excellent high absorption rate, high fixation rate and high lifting power, and their hydrolyzed dyes are easy to remove.
3. Reasonable dyeing and finishing technology
In addition to the correct selection of dyes, reasonable dyeing and finishing technology 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. The wool effect of the dyed semi-finished product directly affects the dye-through property when the dye is dyed. The better the dye-through property, the better the dye will diffuse into the fiber after dyeing, which will help reduce the accumulation of dye on the surface of the fabric. Adding penetrants and mercerizing treatments are beneficial to improving wet rubbing fastness.
The degree of washout of floating dyes is related to their directness to the fiber. Vinyl sulfone-based dyes, which are the most substantive, are the most difficult to remove, followed by hydrolyzed dyes.
The unreacted β-sulfate vinylsulfone dye has the least directness due to the presence of sulfate water-soluble groups, and is the easiest floating dye to remove. Floating colors, electrolytes, and alkalis can be removed by washing with water and soaping. The additives used for soaping must have good penetrating ability, be easily affinity with the dye, and form micelles, which will reduce the affinity between the dye and the fiber and form a core to make the dye micelles disperse stably in the water. You can choose additives composed of anionic and nonionic surfactants with penetrating and dispersing functions, otherwise the effect of completely removing floating colors will not 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, seriously affecting the removal of the floating dye. The drying method is also very important. The amount of dye molecules transferred in contact drying is higher than that in non-contact drying.
4. Control of ph value of dyed fabrics
The amount of alkali used in the dyeing process of deep-concentrated fabrics with reactive dyes is relatively high, and water washing must be strengthened. The ph value of dyed fabrics should be controlled at 6.5-7.5 (the technical standards of Oeko-Tex standard 100 are ph values 4.0-7.5 and 4.0-9.0) to prevent the alkaline medium from breaking the ether bond between the vinyl sulfone group and the fiber. fade.
5. Surface finish of dyed fabric
The worse the surface finish of dyed fabric, the greater the friction coefficient with the white cloth used for testing, and the effective contact surface also increases. Therefore, the wet rubbing fastness decreases. Eco-Label stipulates that the wet rubbing fastness is at least level 2~3, but denim denim is allowed to be level 2 because twill fabric is smaller thanThe friction coefficient of textured cloth is large. Under all conditions being the same, the order of wet rubbing fastness of dyed fabrics is:
Sateen fabric<Poplin fabric<Plain fabric<Twill fabric<Fleece fabric<Calendered fabric<Conventional fabric<Raised fabric
6. Fabric strength damage
Many finishing agents, while improving the function, will damage the fabric strength, such as durable no-iron resin initial shrinkage, flame retardants and sanitary finishing agents, etc., which will reduce the degree of polymerization (DP) of cotton fibers. This increases the number of colored fiber particles and reduces the wet rubbing fastness.
7. Special fixing agent
Special fixing agent can improve the wet rubbing fastness of deep-concentrated reactive dye dyed cloth by 0.5-1.0 levels. The requirements are as follows:
(1) Film-forming The polymer compound is generally polyurethane or silicone with functional groups (-OH, -NH2), and a cross-linking agent is used to cross-link the polymer to make it durable and fast film-forming. (2) No discoloration, no yellowing, and no reduction in sunlight fastness. (3) It can reduce the friction coefficient of fabrics and improve the feel of fabrics. (4) The breathable and moisture-permeable performance of cotton fabrics is still maintained.
In addition to the above improvement measures, an additive company has recently launched additives that can improve wet rubbing fastness. These additives are polymer compounds containing -OH, -NH2 and other functional groups, using ethylene oxide containing The alkyl end-group cross-linking agent quickly forms a film on the surface of the fabric to isolate the dye accumulated on the surface of the fabric from contact with the test white cloth of the abrasion resistance tester. This type of polymer compound also functions as a softener, reducing the film-forming coefficient. When measuring the rubbing fastness, it slows down the frictional resistance between the test cloth and the fabric, thus improving the wet rubbing fastness of the fabric. For example, the following molecular structure of silicone polymer compounds:
This type of auxiliary forms quickly on dyed fabrics The durable film will not reduce the sun fastness, has no discoloration, and has a soft function. </p
