2.2 Factors affecting color fastness
Dyeing fastness refers to the ability of dyed products to maintain their original color and luster under the action of external factors during use or post-dyeing processing.
There are many factors that affect the color fastness, mainly including the chemical composition of the dye, the physical state of the dye on the fiber (such as the degree of dispersion or aggregation of the dye, the crystalline form of the dye on the fiber, etc.), dye concentration, dyeing method, process conditions, Fiber properties, etc. There are also many types of color fastness, mainly including light fastness, washing fastness, chlorine fastness, and rubbing fastness. The following only analyzes its influence on the dyeing fastness of reactive dyes from several main factors.
2.2.1 Light fastness
Light fastness refers to the ability of a dyed object to remain unfading under sunlight. The fading of reactive dyes by light is a very complex photo-oxidation reaction.
There are many factors that affect light fastness: generally reactive dyes such as azo, metal complex, phthalocyanine, and aminoanthraquinone with pyrazolone structure have higher light fastness; dyes that have been bonded to fibers The light fastness is higher than that of hydrolyzed dyes and unreacted dyes; the light fastness of dark colors is higher than that of light colors; the light fastness of dyes diffused evenly in the fiber is high; usually pad-dyed pile dyeing is fast to light The fastness is high; the light fastness of the one-bath pad dyeing and curing method is low.
In addition, the red component in the three primary colors of reactive dyes, because its parent structure is mostly azo, has low light fastness, resulting in asynchronous fading of the three primary colors in the light fastness test, resulting in fading due to visual addition. It is also an important reason for the low light fastness of reactive dyes.
2.2.2 Washing fastness
Washing fastness refers to the fastness of dyed objects when they are washed in soap and other solutions. The washing fastness of reactive dyes is related to the stability of the dye-fiber bond.
The first factor affecting the washing fastness of the dye is the reactive group of the dye. Generally, the covalent bonds formed by s-triazine and diazine reactive dyes and fibers are easily hydrolyzed under acidic conditions, while vinylsulfone-type reactive dyes form covalent bonds with fibers, which are easily hydrolyzed under alkaline conditions; followed by dye liquor The pH value of the dye-fiber bond is the best when the pH value is 6-7. When the pH value increases or decreases, the stability of the dye-fiber bond decreases. It is the temperature of the medium again, the temperature increases, and the hydrolysis of dye-fiber bonds accelerates. In the post-treatment process of dyeing, the washing and soaping is not sufficient, the floating color is not completely removed, and the washing fastness will also decrease.
2.2.3 Fastness to chlorine bleaching
The chlorine bleaching fastness of reactive dyes is mostly poor, which is mainly related to the dye parent: generally pyrazolone and bromoamino acid reactive dyes have poor chlorine bleaching fastness, and phthalocyanine dyes have poor chlorine bleaching fastness. medium. In addition, the reactive groups and water-soluble groups of reactive dyes also have an effect on the fastness to chlorine bleaching of the dyes.
2.2.4 Wet rubbing fastness of reactive dyes
The wet rubbing fastness of reactive dyes is not very good, especially for deep dark dyeings, the reason is the floating color transfer of reactive dyes and the mechanical rubbing transfer of colored nits. This floating color transfer and the transfer of colored nits are related to the structural properties of the dye, the dyeing process, the fabric variety and the dyeing auxiliaries.