How to dye polyester fabrics?
In high temperature and high pressure dyeing, the dyeing process of disperse dyes on polyester fibers can be divided into the following stages:
(1) The disperse dyes gradually approach the fiber interface with the flow of the dyeing solution in the dyeing solution. At this stage, the nature and state of the disperse dyes are basically irrelevant. The dissolved dye molecules and the suspended dye particles are the same with the dyeing solution and the transfer speed Determined by the solution flow rate.
(2) Because there is a dynamic boundary layer that is not easy to flow on the fiber surface, when the disperse dye enters the dynamic boundary layer and approaches the fiber interface, it mainly depends on its own diffusion to approach the fiber. The transfer speed at this stage is not only related to the flow rate of the solution, but also related to the diffusion speed of the disperse dye. Therefore, the dissolved dye molecules diffuse much faster than the suspension and aggregates. The solubility and dispersion state of the disperse dye affect the transfer speed of this stage. Have a greater impact.
(3) When the disperse dye is close to the fiber interface and the molecular force between them is large enough, the disperse dye is quickly adsorbed on the fiber surface. The transfer speed at this stage is mainly determined by the structure and properties of the fibers and dye molecules, and is also related to the nature of the interface solution. Among them, the solubility and dispersion state of the dye have a greater impact. The higher the solubility of the dye and the greater the interaction between the dye molecule and the fiber, the faster the adsorption speed.
(4) After the disperse dyes are adsorbed on the fiber surface, a concentration difference or internal and external dye chemical position difference occurs in the fiber, and the dye will diffuse into the fiber. The diffusion speed here is mainly determined by the fiber chemistry and microstructure, as well as the dye molecules. Structure and concentration are related. The fiber has a higher content of amorphous regions, large pores or more free volume, high dye solubility, and fast diffusion. Therefore, the dye diffusion rate at this stage is directly related to the degree of swelling or plasticization of the fiber and the concentration of disperse dye in the fiber. . The degree of swelling or plasticization is high, and the concentration of the disperse dye in the outer layer of the fiber is high, and the diffusion is fast.
It can be seen from the above that the dyeing speed is not only determined by the structure of the dye and fiber, but also related to the solubility of the dye in the solution and the degree of swelling or plasticization of the fiber during dyeing.
Polyester fiber is a hydrophobic synthetic fiber. The molecular structure of polyester lacks active groups that can bind with dyes like cellulose or protein fibers. Polyester molecules are arranged relatively tightly, and there are only small voids in the fiber. When it is low, the molecular thermal motion changes its position to a small extent. Under humid conditions, polyester fiber will not increase the gap through violent swelling like cotton fiber, and it is difficult for dye molecules to penetrate into the fiber. Therefore, increasing the degree of plasticization of the fiber will help the dyeing process. In addition, the solubility of disperse dyes in water is very low, and the dyes in the dyeing solution must be dispersed in the dyeing bath in suspension by a large amount of dispersant. When dyeing polyester fiber, in order to achieve better dyeing effect, it is usually necessary to add a certain amount of dyeing auxiliaries. The functions of these dyeing auxiliaries in the dyeing process are multifaceted, mainly including:
(1) Appropriately increase the solubility of disperse dyes;
(2) Promote the adsorption of disperse dyes on the fiber surface;
(3) Plastify the fiber or increase the degree of swelling to accelerate the diffusion rate of disperse dyes in the fiber;
(4) "Improve the dispersion stability of the dye.
Generally, the auxiliaries used in high-tamp and high-pressure dyeing of polyester fibers contain a carrier that plasticizes the fiber, a surfactant that solubilizes disperse dyes or stabilizes the dye suspension, and the like. Dyeing auxiliaries polyester fiber dyeing plays a very important role. Polyester fibers and filament fabrics have strong hydrophobicity. The usual dyes and dyeing methods can hardly be dyed and can only be dyed with disperse dyes. But the whole process of such dyeing can only be completed under high temperature and high pressure.