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Analysis of Auxiliaries for Dyeing and Printing of Synthetic Fibers
Time:2019-3-6 15:53:01  Read:733
In synthetic fiber printing and dyeing, surfactants are mainly used as leveling agent, retarder and dispersant.

The molecular structure of polyester fibers is very compact, so it is necessary to use additives to relax and expand the molecules of the fibers in order to achieve the purpose of easy diffusion of dyes. Generally, non-ionic surfactants have good migration property to disperse dyes, but their dispersibility is poor, and they are easy to agglutinate dye particles. Anionic surfactants have good dispersibility, but poor migration. Therefore, the practical application of fast leveling agents is mostly a mixture of non-ionic surfactants and anionic surfactants.

Leveling involves the uniform distribution of dyes between fibers and within fibers. The role of surfactants can be conceived as two mechanisms. The basic principles are to delay the adsorption of dyes and slow down the dye uptake: 1) competition between dyes and surfactants for dye holders on the surface of fibers. 2) The interaction between dyes and surfactants in dyeing bath.

Usually in the process of dye processing, surfactants as dispersants are fully mixed with dyes, and dispersants can also be added to the dyeing bath. Dispersants play two main special roles in dyeing: one is the anti-flocculation effect of dismantling aggregated particles; the other is the ability to maintain the stability of dispersed particles.

In high temperature dyeing of polyester fibers with disperse dyes, anionic surfactants were added as dispersants, which increased the solubility of dyes several times due to solubilization. The dispersant can not only prevent the growth of dye particles (inhibit the growth of crystallization) at high temperature and pressure, but also keep the dispersity of disperse dyes. It can also help the dyes diffuse into polyester fibers and prevent the coking of dyes. In addition, the dispersant also has the characteristics of non-inhibition of final dyeing, small dye discoloration, small foaming, and in fact slow dyeing and leveling, and does not affect the dyeing fastness. In order to improve the stability of disperse dyes in dyeing bath, surfactants should be added when polyester fibers are dyed with disperse dyes. If dyeing at 130 C, polycyclic anionic surfactants are superior to less cyclic anionic surfactants in terms of affinity for disperse dyes, but excessive use of surfactants will inhibit dyeing and even decompose azo disperse dyes. Non-ionic surfactants can improve the solubility of disperse dyes in water, help dye migration, improve the levelness and permeability of dyeing, and improve the uptake rate of dyes with high fastness and high relative molecular weight. However, when dyeing at high temperature beyond the cloud point, non-ionic surfactants cooperate with dyes to settle on the fibers, which easily results in contamination of impurities such as spots and tars. This phenomenon can be overcome by adding anionic surfactants to improve the cloud point. Modified non-ionic surfactants without cloud point and non-ionic surfactants with large molecular number of ethylene oxide can also be used as leveling agents.

The main anionic surfactants used as dispersant are naphthalene sulfonate formaldehyde condensate, lignin sulfonate, cresol sulfonate formaldehyde condensate, alkyl phenol ethylene oxide-propylene oxide block polyether, nonylphenol polyoxyether, N-methyl-N-(beta-hydroxyethyl) laurylamide, etc. Surfactants can be used as dispersants alone or in combination.