Thermal migration of disperse dyes is not the redistribution of dyes in the fiber and surface solvent phases under dry heat conditions, but its inherent physical properties, which also causes the color fastness of polyester-containing fabrics to decrease during dry heat treatment after dyeing. and color light variation.
Key factors
By analyzing the dyeing temperature, heat treatment temperature and time, and the sublimation property of the dye , surfactants and finishing agents, dyeing methods and the influence of heat setting on the thermal migration of dyes. Try to use high temperature pre-setting before dyeing, non-contact hot air drying below 130℃ and low temperature soft drawing process, as well as low temperature and slow resin A number of countermeasures including finishing processes are adopted 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.
Thermal migration of disperse dyeing
Polyester fiber dyed with disperse dyes during dry heat treatment , resulting in a decrease in color fastness and color variation. 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 dissolve in the fiber and the solvent attached to the surface of the fiber (the surface that dissolves the disperse dyes under dry heat conditions). Active agents, softeners, resins, antifouling agents, antistatic agents, etc.) are the distribution phenomena 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 structure of the polyester fiber changes. During relaxation, the disperse dye diffuses from the surface of the fiber into the interior of the fiber, and mainly acts 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 to relax again. , resulting in the weakening of the binding force between some dye molecules and the long polyester chain. 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.
3. During the wet fastness test. 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.
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 inside 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..
2. The relationship between heat treatment temperature and thermal migration
Under normal conditions, after dyeing The higher the temperature of dry heat treatment, the greater the thermal migration of the dye, and the more serious the impact on the shade and color fastness of the dye. When heat treated below 130°C, the thermal migration of the dye is not great; when heat treated above 130°C, the thermal migration of the dye is significantly enhanced.
3. The relationship between heat treatment time and thermal mobility
Baking time is between 20 and 40S Within the range, the migration amount of dyes increases sharply with the extension of time; in the range of 40 to 50S, the thermal migration amount of dyes 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 dye sublimation and thermal migration
Some sublimation resistance Some good high-temperature dyes have small thermal migration (such as dispersed gray S-BN), and some have large thermal migration (such as dispersed red S-3GFL, dispersed deep 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
