Discussion on dyeing fastness of reactive dyes and disperse dyes

Reactive dyes and disperse dyes are the most important dyes for cellulose fibers and polyester fibers. The output of these two dyes in the world accounted for 23.6% and 26.3% of the total output of dyes, respectively. However, some fastnesses of their dyes are often difficult to meet trade requirements and international and domestic standards, such as light-colored fastnesses of reactive dyes, water washing fastnesses of dark colors and wet rubbing fastnesses, thermal migration fastnesses of disperse dyes, etc.
1, fastness to light of reactive dyed light coloured dyed fabrics
Reactive fading mechanism
Light fading of reactive dyes is a very complex photooxychlorination reaction. Knowing the mechanism of photofading, the molecular structure design of dyes consciously creates some obstacles to photooxidation reaction and delays photofading. For example, yellow dyes containing dolsulfonic group and pyrazolone, blue dyes containing phthalocyanine methyl and bisazo trichelate rings, and red dyes containing metal complexes, but still lack bright red dyes with light fastness.
The fastness to sunlight of dyed fabrics varies with dyeing concentration. The fastness to sunlight of fabrics dyed with the same dye on the same fiber increases with dyeing concentration. The fastness to sunlight of light-colored fabrics decreases with low dyeing concentration. However, the fastness of common dyes to sunlight on printed dye cards is measured at a dyeing concentration of 1/1 (i.e. 1% OWF or 20-30g/l dye concentration). If the dyeing concentration is 1/6, 1/12 or 1/25, the fastness to sunlight will be greatly reduced.
Some people have suggested that it is not advisable to use ultraviolet absorbent to improve the fastness to sunlight. Ultraviolet radiation needs to be used a lot, and can only be improved by half, and the cost must be improved a lot. Therefore, only fair dyes can be used to solve the problem of sunlight fastness.
2, wet rubbing fastness of reactive dyed dyed fabrics
The main reasons for the divergence of wet rubbing fastness of deep-colored textiles with reactive dyes are the floating color transfer of water-soluble reactive dyes and the mechanical friction transfer of non-ferrous fiber particles. The measures to improve the dyeing of textiles with deep concentrated reactive dyes must be comprehensively solved from the selection of dyes, dyeing process, kinds of fabrics and the addition of special auxiliaries.
In order to reduce the float of dyed fabrics, it is necessary to select a dye with a fixing rate of more than 70% and a difference of the ultimate dyeing rate and fixing rate of less than 15%, so that the float can be easily removed at a dyeing rate of no more than 75%. In addition, a dye with high dye lifting power should be selected, that is to say, the amount of dye used in deep-concentrated dyeing should not exceed the fiber saturation. And adsorption capacity of 10%.
Dyeing process is also very important. Removal of float is the key. Hard water is not conducive to removal of float. It must be softened. It is best to use non-contact drying. Functional finishing can damage the fabric strength and increase the particle size of non-ferrous fibers. It must be controlled to a minimum. Finally, the wet rubbing fastness of dyed fabrics with deep concentration of reactive dyes can be improved by 0.5-1.0 grade if treated with a special assistant for improving wet fastness.
3, the decrease of fastness caused by heat transfer after dyeing with disperse dyes.
Principle of dispersed heat transfer
Thermal migration after dyeing refers to the thermal migration of disperse dyes after dyeing polyester fibers at high temperature (stretching and setting) due to the influence of surface auxiliaries. Dyes migrate from the inside of the fibers to the surface of the fibers through the expanded capillaries of the fibers, resulting in the accumulation of dyes on the surface of the fibers, resulting in a series of fastness deterioration. This phenomenon may also occur in the long-term storage and transportation of dyed textiles and clothing. It is a redistribution phenomenon of disperse dyes in polyester fibers and additives. It is different from the sublimation fastness of disperse dyes, which is called thermal migration fastness.
This phenomenon is caused by the extensive application of amino silicone oil microemulsion softener containing a large number of non-ionic surfactants in textiles in the past 20 years. The solution is to replace the macroemulsion amino silicone oil with a small amount of emulsifier and the self-emulsifying hydrophilic amino silicone oil without emulsifier. At the same time, disperse dyes with heat transfer resistance, such as Foron S-WF and Dispereol XF with special structure, are introduced in Europe, which make dyed dyes have high affinity with polyester fibers and difficult to migrate from the inside of fibers to the surface at high temperature, thus resolving the fastness decline caused by heat transfer.