1 Effect of disperse dye dyeing
Thermal migration of disperse dyes is not the redistribution of dyes in the fiber and surface solvent phases under dry heat conditions, but the redistribution of dyes in the fiber and surface solvent phases. The inherent physical properties also cause the color fastness to decrease and the color light to vary during dry heat treatment of polyester-containing fabrics after dyeing.
Key factors: The thermal migration of dyes by analyzing dyeing temperature, heat treatment temperature and time, dye sublimation properties, surfactants and finishing agents, dyeing methods and heat setting To minimize the impact of thermal migration of dyes, we should try to adopt multiple countermeasures such as high-temperature pre-styling before dyeing, non-contact hot air drying below 130°C, low-temperature soft drawing process, and low-temperature slow resin finishing process to minimize the impact of thermal migration of dyes. .
After polyester fabrics (pure polyester fabrics or polyester-cotton, polyester-viscose and other interwoven and blended fabrics) are dyed with disperse dyes (especially darker colors dyed by high temperature and high pressure method), after 130 Dry heat treatment above ℃,
such as post-dyeing thermal stenter setting, resin baking, etc., usually requires varying degrees of changes in the following three aspects, such as dyeing fastness (Soaping, friction, and sun exposure) are significantly reduced, generally medium and dark colors are reduced by 0.5 to 1.5 levels; the color of the cloth surface changes to varying degrees; polyester-cotton, polyester-viscose and other interwoven or blended fabrics, the contamination of the cotton-viscose component will Significant increase.
2 Thermal migration of disperse dyeing
Dyeing with disperse dyes During the dry heat treatment of polyester fiber, the color fastness 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 dry heat treatment above 130°C after dyeing with disperse dyes. It is generally believed that the thermal migration of disperse dyes is due to the fact that the dyes move between the fibers and the solvents attached to the surface of the fibers (surfactants, softeners, resins, antifouling agents, antifouling agents, and antifouling agents that dissolve disperse dyes under dry heat conditions). electrostatic agent, etc.) 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 is inconsistent with reality.
For example, after pure polyester fabric is dyed at high temperature and high pressure without any post-processing, it is fully washed with hot and cold water, dried, and directly dry-heat treated at 180°C for 35 seconds. The thermal migration phenomenon will still remain. Very significant. Thermal migration is an inherent physical property of disperse dyes. An attachment phenomenon that is not caused by the presence of a second phase solvent.
The process of thermal migration of disperse dyes can be explained as follows:
① During the high-temperature dyeing process, the polyester fiber structure becomes relaxed , disperse dyes diffuse from the surface of the fiber into the interior of the fiber, and mainly act on the polyester fiber through hydrogen bonding, dipole attraction and van der Waals forces.
② When the dyed fiber is subjected to high-temperature heat treatment, the heat energy gives the long polyester chain higher activity energy, causing the molecular chain vibration to intensify, and the microstructure of the fiber relaxes again. As a result, the binding force between some dye molecules and the long polyester chains is weakened. Therefore, some dye molecules with higher activity energy and higher degree of self-possession migrate from the inside of the fiber to the fiber surface with a relatively loose structure, and combine with the fiber surface to form surface dyes, or adhere to adjacent cotton viscose groups. point.
③During the wet fastness test process. Surface dyes that are not firmly combined, as well as dyes that adhere to the cotton adhesive component, can easily break away from the fiber and enter the solution, contaminating the white cloth; or they can directly adhere to the test white cloth through friction, thus showing the wet fastness and friction of the dye. Fastness decreases.
3 Why is the fastness of disperse dyeing poor?
Disperse dyeing mainly involves high temperature and high pressure when dyeing polyester fiber. Although disperse dye molecules are small, there is no guarantee that all dye molecules will enter the interior of the fiber during dyeing, and some disperse dyes will adhere. On the surface of the fiber, it causes poor fastness. Reductive cleaning is used to destroy the dye molecules that have not entered the interior of the fiber to improve the fastness and improve the color and light.
Polyester fabrics are dyed with disperse dyes, especially in medium and dark colors. In order to fully remove floating colors and oligomers remaining on the surface of the fabric and improve the dye fastness, it is usually necessary to Restorative cleaning is required. Blended fabrics generally refer to yarns blended from two or more components, so this fabric has the advantages of these two components. And you can get more properties of one ingredient by adjusting the ingredient ratio.
Blending generally refers to short fiber blending, that is, two fibers with different components are mixed together in the form of short fibers. For example: polyester-cotton blended fabric, also usually called T/C, CVC, T/R, etc. It is made of polyester staple fiber and cotton fiber or man-made fiber blended yarn. Its advantages are: it has the appearance and feel of cotton cloth, weakens the chemical fiber luster and chemical fiber feel of polyester cloth, and improves the layering.
Improved color fastness. Since polyester fabric is colored at high temperature, the color fastness is higher than that of pure cotton. Therefore, the color fastness of polyester-cotton blended fabric is higher than that of pure cotton. The color fastness of cotton is also improved. However, in order to improve the color fastness of polyester-cotton fabrics, reduction cleaning (the so-called R/C) must be done, which is post-processing after high-temperature dyeing and dispersion. Only after restoration cleaning can the ideal color fastness be achieved.
Short fiber blending allows the characteristics of each component to be evenly exerted. In the same way, blending of other components can also exert their respective advantages to achieve�The relationship between thermal migration
When the baking time is in the range of 20 to 40S, the migration amount of the dye increases sharply with the extension of time; in the range of 40 to 50S, the migration of the dye The thermal migration amount does not increase significantly; beyond 50S, the thermal migration amount of low-temperature and medium-temperature disperse dyes decreases instead. Obviously, this is related to the increased sublimation of the dye.
4. The relationship between sublimation and thermal migration of dyes
Some high-temperature dyes with good sublimation resistance include Some have small thermal migration (such as dispersed gray S-BN), while some have large thermal migration (such as dispersed red S-3GFL, dispersed dark blue HGL, etc.). Some low-temperature and medium-temperature dyes with poor sublimation resistance (such as Disperse Red B, Fulon Brilliant Red E-RLN, etc.), judging from the results of parallel measurements, their thermal migration is smaller, which is related to the sublimation property of the dye. Very relevant. Therefore, there is no obvious rule between the sublimation and thermal migration properties of dyes. </p
