Dyeing of disperse dyes

The influence of disperse dyeing

The thermal migration of disperse dyes is not the redistribution of dyes in the two phases of fiber and surface solvent under dry heat conditions, but its inherent physical characteristics, which also cause the color fastness and shade variation of polyester-containing fabrics to decrease during dry heat treatment after dyeing. .

Key factors: through analysis of dyeing temperature, heat treatment temperature and time, dye sublimation, surface active agent and finishing agent, dyeing method and the influence of heat setting on dye thermal migration, try to use pre-dyeing high temperature preset type, 130℃ The following non-contact hot-air drying and low-temperature soft drying process, as well as low-temperature slow-speed resin finishing process and other countermeasures, in order to control the thermal migration of dyes to a minimum. 

Polyester fabrics (pure polyester fabrics or polyester-cotton, polyester-viscose and other interwoven or blended fabrics) are dyed with disperse dyes (especially dyed with darker colors by high-temperature and high-pressure methods), and then subjected to dry heat treatment above 130°C. 

For example, after dyeing, heat stenter setting, resin baking, etc., the following three aspects usually have different degrees of changes, such as dyeing fastness (soaping, friction, sun exposure) is significantly reduced, and generally medium and dark colors are reduced by 0.5 ～1.5; the color of the cloth surface changes to different degrees; the pollution of the cotton and viscose components of polyester-cotton, polyester-viscose and other interwoven or blended fabrics will increase significantly.

Disperse dyeing thermal migration

In the process of dry heat treatment, the color fastness of polyester fibers dyed with disperse dyes decreases and the color light changes. It is 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 also 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, thermal migration will not occur. In fact, this explanation does not correspond to 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. It is 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:

①During the high-temperature dyeing process, the structure of the polyester fiber becomes loose, and the 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.

②When the dyed fiber is subjected to high temperature heat treatment, the heat energy gives the polyester long chain higher activity energy, which intensifies the molecular chain vibration, and the fiber's microstructure relaxes again, resulting in the binding force between part of the dye molecule and the polyester long chain. Weaken. 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.

③During the wet fastness test. Surface dyes that are not firmly bonded, and dyes that adhere 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, thus showing the wet fastness and rubbing of the dyed product The fastness decreases.