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 fabric.
The floating dyes of reactive dyes include dyes that have been adsorbed on the fibers without reacting with the fibers, partially hydrolyzed dyes, and vinylsulfone-based dyes that have eliminated sulfates. The total amount of floating dyes can be represented 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, it is necessary to select reactive dyes with less floating amount after dyeing, that is, dyes with low E-F value, in order to remove the floating color. If the fixation rate is high, the dye is fixed to the fiber after dyeing, and the amount of floating color can be greatly reduced.
2. Choose reactive dyes with high lifting power
The concentration of dyes used in deep dyeing is high, and the amount of floating dyes increases. The fiber has a saturation value for dye adsorption, and the dye concentration should generally not exceed 10% of the dyeing saturation value. Excessive dye cannot be dyed and fixed, and will accumulate on the surface of the fabric, thereby affecting the wet rubbing fastness of the dyed product. Reactive dyes with high lifting power must be selected for deep dyeing.
3. Reasonable dyeing and finishing process
In addition to the correct selection of dyes, reasonable dyeing and finishing processes 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 hair effect of the dyed semi-finished products directly affects the dye penetration of the dye. The better the penetration, the better the diffusion of the dye into the fiber after dyeing, which is beneficial to reduce the accumulation of dye on the surface of the fabric. The addition of penetrant and mercerizing treatment are beneficial to improve the wet rubbing fastness.
Water quality is a very important factor. If the water quality is high in hardness, the water-soluble groups of floating dyes will form lakes that are difficult to dissolve in water, which will seriously affect the removal of floating dyes. The drying method is also very important. The amount of dye molecules transferred by contact drying is higher than that of non-contact drying.
4. Control of pH value on the surface of dyed fabric
In the process of dyeing deep and dense fabrics with reactive dyes, the amount of alkali is relatively high and washing must be strengthened. The pH value of the dyed fabric surface should be controlled at 6.5-7.5 (Oeko-Tex standard 100 technical standards are pH 4.0-7.5 and 4.0-9.0) to prevent the ether bond between the vinyl sulfone group and the fiber from being broken by the alkaline medium. fade.
5. Surface finish of dyed fabric
The worse the surface finish of the dyed fabric is, the greater the coefficient of friction between it and the white cloth used for testing and the larger the effective contact surface. Therefore, the wet rubbing fastness decreases. Eco-Label stipulates that the wet rubbing fastness is at least 2~3 grades, but denim denim is allowed to be grade 2 because the friction coefficient of twill fabric is larger than that of plain weave fabric.
6. Strong damage to the fabric
Many finishing agents can damage the strength of the fabric while improving their functions. For example, durable non-iron resin shrinkage, flame retardants and sanitary finishing agents, etc., reduce the degree of polymerization (DP) of cotton fibers, thereby increasing the colored fiber particles and making The wet rubbing fastness decreases.
7. Special fixing agent
The special fixing agent can improve the wet rubbing fastness of fabrics dyed with deep and concentrated reactive dyes by 0.5-1.0 grade, and its requirements are as follows:
(1) The polymer compound that can form a film is generally polyurethane or silicone with functional groups (-OH, -NH2), and has a cross-linking agent to cross-link the polymer to make it durable and rapid. Membranous.
(2) No color change, no yellowing, and no reduction in light fastness.
(3) It can reduce the friction coefficient of the fabric and improve the feel of the fabric.
(4) Maintain the breathability and moisture permeability of the cotton fabric.