Principles and applications of various leveling agents

Leveling agentsshould have the following features: enabling the dye to be slowly adsorbed by the fiber (having a slow dyeing effect); if the dyeing is uneven, the dye can be moved from the dark part to the light part (having a transfer effect); and the dyeing fastness should not be reduced.

1. Principle of leveling: Leveling agents can be divided into fiber-affinity leveling agents, dye-affinity leveling agents, and leveling agents with affinity for both dyes and fibers according to different principles of action.

2. Principle of fiber-affinity leveling When the affinity of the leveling agent to the fiber is greater than the affinity of the dye to the fiber, the leveling agent and the dye compete with the fiber for dyeing. The leveling agent preferentially combines with the fiber, occupies the dyeing seat on the fiber, hinders the combination of the dye and the fiber, and delays the dyeing of the dye. However, the binding force is not as strong as the dye molecule. As the temperature of the dye bath increases, the dye gradually displaces the leveling agent from the fiber, and finally the dye occupies the dyeing seat, thereby achieving the purpose of leveling. Slow dyeing effect: The leveling agent preferentially combines with the fiber, occupies the dyeing seat on the fiber, hinders the combination of the dye and the fiber, and delays the dyeing of the dye. Once the dyeing operation is completed, the dye of this type of fiber-affinity leveling agent is fixed on the fiber and cannot move, so it has no ability to transfer dyeing. Leveling agents that have affinity for fibers are called fiber-affinity leveling agents.

Fiber-affinity leveling effects often occur in the following dyeing processes: ① Anionic leveling agents in the dyeing process of natural fibers and nylon fibers; ② Cationic leveling agents in the dyeing process of acrylic fibers. When cationic leveling agents are used in acrylic dyeing, the leveling agent and the dye compete for the acidic base of the fiber and occupy the dyeing seat on the fiber before the dye, which plays a role in inhibiting the absorption of the dye in the initial stage of dyeing. During the heating process, the leveling agent is desorbed and the dye molecules slowly go to the dyeing seat to achieve a uniform dyeing result. Among the leveling agents with affinity for fibers, those used for natural fibers and nylon fibers are anionic surfactants containing acidic groups, which are mainly sulfonated oils and sodium salts of higher alcohol sulfates. Cationic surfactants used for acrylic fibers are mainly quaternary ammonium salts.

2. Principle of action of dye-affinity leveling agents When the affinity of the leveling agent for the dye is greater than the affinity of the dye for the fiber, before the dye is adsorbed by the fiber, the leveling agent first pulls the dye and then combines to form a certain stable aggregate. The dye must be separated from the leveling agent before it can combine with the fiber, thereby reducing the dye mobility and diffusion rate and delaying the dyeing time. At high temperatures, this stable aggregate comes into contact with the fiber, decomposes, and then releases the dye, and then combines the dye with the fiber, thereby achieving the purpose of leveling. Delayed dyeing effect: The leveling agent combines with the dye, hinders the combination of the dye and the fiber, delays the dyeing of the fabric, and can pull part of the dye on the dark color back to the dye bath, and then transfer it to the light color to achieve leveling. Therefore, this leveling agent has a migration effect, so it can be used as a stripping agent. Dye-affinity leveling agents are mainly polyethylene glycol ether-type nonionic surfactants. The dye-affinity of this leveling agent is due to the fact that the ether bond of polyethylene glycol is easy to combine with the nitrogen atoms of the hydroxyl and amino groups on the dye.

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