Disperse dyes
Disperse dyes are a kind of dyes developed with the development of synthetic fibers. In 1921, they were industrialized in acetate fibers. In order to solve the problem of dyeing with water-soluble dyes, Baden aniline soda ash company of Germany produced a kind of dyes with strong hydrophobicity the following year, which was called acetate dyes at that time. This kind of dyes are still water-soluble dyes. Later, the British BRC company introduced a slurry dye, which dispersed the water-insoluble SRA dye in sulfonated ricinolic acid, officially opening the development of disperse dyes. With the continuous development of synthetic fiber, the performance of disperse dyes is also improving. It has increased to 1819 varieties in 1971. At present, disperse dyes have become a large class of dyes with complete chromatography and a wide variety of categories.
Disperse dyes are a kind of non-ionic dyes with small molecules. They do not contain water-soluble groups such as sulfonic acid groups, but only some weak polar groups such as hydroxyl, amino and nitro groups. Therefore, the solubility of these dyes in water is very low. During dyeing, the dyes are evenly dispersed in the dye solution in the state of fine particles with the help of dispersant. Polyester fiber has strong hydrophobicity and poor hygroscopic swelling performance, so it can not be dyed with general water-soluble dyes. Disperse dyes have small molecular structure and hydrophobic characteristics, have a certain affinity for polyester fiber, and the molecular structure is small, which is conducive to diffusion in the fiber. They are stable under high-temperature dyeing conditions, and have become a special dye for polyester fiber.
Dyeing principle and process of polyester fiber
In the dyeing process of disperse dyes, the disperse dye particles in the dye solution dissolve to form single molecule disperse dyes. The diffusion and adsorption process of dye molecules with the dye solution to the fiber surface is similar to the dyeing process of reactive dyes. The swelling degree of polyester fiber in water is very small, and only part of the volume in polyester fiber that is not occupied by fiber molecular segments, that is, the free volume, is below the glass transition temperature of polyester fiber, The free volume is distributed among the molecular chains in the amorphous region of the fiber in the form of tiny holes. When the dyeing temperature reaches above the glass transition temperature, the movement of the molecular chain segments of the fiber intensifies and forms instantaneous space-time holes. The disperse dye can transition in these holes and diffuse into the fiber from the high concentration region of the dye to the low concentration region
Because disperse dyes must be above the glass transition temperature when dyeing polyester fiber, the commonly used disperse dye dyeing processes include high temperature and high pressure dyeing and hot melt pad dyeing. The former belongs to intermittent production and is not suitable for mass production. The latter belongs to continuous production and has the characteristics of high production efficiency. In the process of high temperature and high pressure dyeing, most of the disperse dyes diffuse into the fiber, but there are still a small number of disperse dyes attached to the fiber surface. Especially when using disperse dyes to dye medium and dark colors, the dye uptake will gradually decrease with the increase of dyeing concentration. Therefore, reduction cleaning process is generally required after dyeing to wash the floating color on polyester fabric and improve color fastness..
