How do disperse dyes work?

Because polyester fiber has the characteristics of strong hydrophobicity, high crystallinity and high alignment, it is difficult to make the dye enter the fiber in the form of single molecule to complete the dyeing of polyester by conventional methods. Therefore, special dyeing methods are required. The methods used are carrier method, high temperature and high pressure method and high temperature hot melt method. These methods use different conditions to expand the fibers and increase the space between the fiber molecules. At the same time, additives are added to increase the diffusion rate of the dye molecules, so that the dye molecules continue to diffuse into the expanded and enlarged fiber spaces. Intermolecular attraction and hydrogen bond fixation complete the dyeing of polyester. Because the solubility of disperse dyes in water is extremely low, it is necessary to rely on the addition of dyes and dispersants in the solution to form the dye liquor. In order to prevent the hydrolysis of disperse dyes and polyester under the action of high temperature and alkali, the dyeing of disperse dyes often needs to be carried out under weak acid conditions.

1. Vector staining method
The carrier dyeing method is carried out by heating under normal pressure. It uses some chemicals that are direct to dyes and fibers. When such chemicals enter the interior of polyester during dyeing, the dye molecules are also carried in at the same time. This chemical is called carrier or dye carrier.
2. High temperature and high pressure dyeing method
The high temperature and high pressure dyeing method is carried out in a humid and hot state under high temperature and pressure. The dyeing rate of the dye is very slow within 100℃. Even if it is dyed in a boiling dyebath, the dyeing rate and dyeing percentage are not high, so the pressure must be below 2atm (2.02×105Pa), and the temperature of the dyebath can be increased to 120～130℃, due to the increase of temperature, the segments of fiber molecules move violently, resulting in more and larger transient pores. At this time, the diffusion of dye molecules is also accelerated, which increases the diffusion rate of dyes to the interior of the fiber, making dyeing possible. The rate is increased until the dye is exhausted and the dyeing is completed. The high temperature and high pressure dyeing method of disperse dyes is an important method, which is suitable for low temperature dyes with low sublimation fastness and small molecular weight. Dyeing with this type of dye has good levelness, bright color, good hand feel, and high degree of fabric penetration. It is suitable for small batch and multi-variety production, and is often used in the dyeing of polyester-cotton blended fabrics.