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Why Is The Dispersion Fastness Poor?

Dec. 17, 2020
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Why Is The Dispersion Fastness Poor?

Disperse dyeing mainly uses high temperature and high pressure when dyeing polyester fibers. Although the disperse dye molecules are small, it cannot guarantee that all the dye molecules enter the fiber during dyeing. Some disperse dyes will adhere to the fiber surface, resulting in poor fastness. It is used to destroy the dye molecules that have not entered the fiber, improve the fastness, and improve the shade.

Disperse dye dyeing of polyester fabrics, 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 fastness of dyeing, it is usually necessary to perform reduction cleaning after dyeing.

Blended fabric generally refers to a yarn made of two or more components blended, so this fabric has the advantages of these two components. And by adjusting the component ratio, more characteristics of one of the components can be obtained.

Blending generally refers to staple fiber blending, that is, two fibers of different components are mixed together in the form of staple fibers. For example: polyester-cotton blended fabric, also usually called T/C, CVC.T/R, etc. It is woven with a blend of polyester staple fiber and cotton fiber or man-made fiber. Its advantages are: it has the appearance and feel of all-cotton cloth, weakens the chemical fiber luster and chemical fiber feel of polyester cloth, and improves the level.

Improved color fastness, because polyester fabric is colored at high temperature, the color fastness is higher than that of cotton, so the color fastness of polyester-cotton blended fabric is also improved compared with cotton.

Disperse dyeing

However, to improve the color fastness of polyester-cotton fabrics, reduction cleaning (the so-called R/C) must be done, and post-treatment after high temperature dyeing and dispersion. The ideal color fastness can only be achieved after reduction and cleaning.

Staple fiber blending allows the characteristics of each component to be evenly displayed. Similarly, other component blending can also play their own advantages to meet some functional or comfort or economic requirements. However, polyester-cotton blended fabrics are dispersed and dyed at high temperatures. Medium, due to the blending of cotton or rayon fiber, and the dyeing temperature can not be higher than the temperature of the polyester fabric. However, polyester-cotton or polyester-cotton rayon fabrics, under the stimulation of strong alkali or sodium hydroxide, will cause the fiber strength or tearing force to drop drastically, and it is difficult to achieve product quality in the subsequent links.

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 by hydrogen bond, dipole attraction and van der Waals force.

2. When the dyed fiber is subjected to high temperature heat treatment, the thermal energy gives higher activity energy to the polyester long chain, which intensifies the vibration of the molecular chain, and the microstructure of the fiber relaxes again, resulting in the bonding between some dye molecules and the polyester long chain 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.

3. During the wet fastness test. Surface dyes that are not firmly bonded, and dyes that adhere to the cotton sticky component, will easily leave the fiber to enter the solution and contaminate the white cloth; or directly adhere to the test white cloth by rubbing, thus showing the wet fastness and friction of the dyed product the fastness decreases.