What is the principle behind affinity-based leveling dyeing?

When the leveling agent's affinity for the fiber is greater than the dye's affinity for the fiber, the leveling agent and dye compete for dyeing. The leveling agent preferentially binds to the fiber, occupying dyeing sites on the fiber, hindering the dye's binding to the fiber, and delaying dye uptake. However, its binding strength is not as strong as that of the dye molecules. As the dyebath temperature increases, the dye gradually displaces the leveling agent, eventually allowing the dye to occupy dyeing sites on the fiber, achieving level dyeing.

Delayed dyeing:

The leveling agent preferentially binds to the fiber, occupying dyeing sites on the fiber, hindering the dye's binding to the fiber, and delaying dye uptake. After dyeing is completed, the dye is fixed to the fiber and cannot migrate, resulting in a lack of dye migration. Leveling agents with an affinity for fibers are called affinity-based leveling agents.

Fiber-based leveling agents are commonly used in the following dyeing processes:

① Anionic leveling agents for dyeing natural fibers and nylon fibers;

② Cationic leveling agents for dyeing acrylic fibers. When used in acrylic dyeing, cationic leveling agents compete with the dye for the fiber's acidic groups, occupying dyeing sites before the dye, thereby inhibiting dye absorption in the initial stages of dyeing. During heating, the leveling agent desorbs, allowing dye molecules to slowly migrate to the dyeing sites, achieving uniform dyeing. Among fiber-friendly leveling agents, those used for natural and nylon fibers are anionic surfactants containing acidic groups, primarily sulfonated oils and sodium salts of higher alcohol sulfates. Cationic surfactants used for acrylic fibers are primarily quaternary ammonium salts.