What is the thermal migration of dispersion dyeing?

In the dry heat treatment process of polyester fibers dyed with disperse dyes, the color fastness decline and shade variation are caused by the thermal migration of disperse dyes.

The so-called thermal migration refers to a phenomenon in which part of the dye migrates from the inside of the fiber to the surface of the fiber during the dry heat treatment process above 130°C after dyeing with disperse dyes. It is generally believed that the thermal migration of disperse dyes is due to the solvent that the dye adheres to the fiber and the surface layer of the fiber under dry heat conditions (surfactants, softeners, resins, antifouling agents, antifouling agents that dissolve the disperse dyes) Electrostatic agent, etc.) the distribution phenomenon in the two phases; it is believed that if there is no second phase solvent on the surface of the fiber, the thermal migration phenomenon will not occur. In fact, this explanation does not match the reality.

For example, after the pure polyester fabric is dyed at high temperature and high pressure, without any post-treatment, it is fully washed with hot and cold water and then dried, and directly dried at 180°C for 35s, the heat migration phenomenon is still very significant. Thermal migration is an inherent physical property of disperse dyes, not a dependency phenomenon caused by the presence of the second phase solvent.

The thermal migration process of disperse dyes can be explained as follows:

(1) In the process of high temperature dyeing, the structure of polyester fiber becomes loose, disperse dye diffuses from the surface of the fiber into the inside of the fiber, and mainly acts on the polyester fiber with hydrogen bond, dipole attraction and van der Waals force.

(2) When the dyed fiber is subjected to high temperature heat treatment, due to the heat energy giving higher activity energy to the polyester long chain, the molecular chain vibration is intensified, and the microstructure of the fiber relaxes again, resulting in some of the dye molecules and the polyester long chain. The binding force is weakened. Therefore, some dye molecules with higher activity energy and higher degree of autonomy migrate from the inside of the fiber to the fiber surface layer with relatively loose structure, combine with the fiber surface to form a surface layer dye, or adhere to the adjacent cotton stick group. point.

(3) During the wet fastness test, the surface dyes that are not firmly bonded and the dyes adhering to the cotton sticky component are easy to leave the fiber and enter the solution, contaminating the white cloth; or directly adhere to the test white cloth by rubbing, This shows that the wet fastness and rubbing fastness of the dyed product have decreased.