Why is the dispersion fastness poor?

Disperse dyeing is mainly used for polyester fiber dyeing at high temperature and high pressure. Although the disperse dye molecules are small, it is not guaranteed that all the dye molecules enter the fiber during dyeing. Some disperse dyes will adhere to the fiber surface, resulting in poor fastness, so do reduction cleaning. It is used to destroy the dye molecules that have not entered the fiber to improve the fastness and improve the color light.

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 yarn blended with 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.

The color fastness is improved. Because the polyester fabric is colored at high temperature, the color fastness is higher than that of cotton. Therefore, the color fastness of polyester-cotton blended fabric is also improved compared with that of cotton. However, to improve the color fastness of polyester-cotton fabrics, reduction cleaning (the so-called R/C) must be done, and post-treatment after dyeing and dispersion at high temperature. 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 blends 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 cannot be higher than the temperature of the polyester fabric. However, polyester-cotton or polyester-cotton man-made fiber cloth will cause the fiber strength or tearing force to drop drastically under the stimulation of strong alkali or sodium hydroxide, and it is difficult to achieve the quality of the product in the subsequent links.

The relationship between dyeing method and thermal migration

When fabrics dyed with disperse dyes are dry heat-treated above 130°C, thermal migration is common. But different dyeing methods have different directions of dye thermal migration.

① Normal pressure boiling dyeing is light-colored ring dyeing. After high temperature dry heat treatment, there is almost no sign of heat migration from the inside to the outside. The dye on the fiber surface layer migrates or diffuses like inside the fiber due to the concentration gradient.

②Hot-melt dyeing dyes are distributed inside the fiber, and there is generally a certain degree of concentration gradient. During high-temperature heat treatment, part of the dye molecules migrate to the inside, and part of the dye molecules move from the inside of the fiber to the surface of the fiber or into the second phase solvent on the surface of the fiber.

③High temperature and high pressure dyeing has good penetrability, and there is almost no gradient in the distribution of dyes in the fiber. Therefore, during high-temperature dry heat treatment, the dye only moves outward in one direction, which has a greater impact on the shade and color fastness of the dyed fabric, especially for dark colors.

The relationship between heat setting and heat migration

The dyes dyed by the fixed and unshaped blanks have the same phenomenon of thermal migration of the dyes during the high-temperature dry heat treatment. The pre-dyeing setting has a certain inhibitory effect on the thermal migration of the dyed product in the dry heat treatment, but this inhibitory effect is directly related to the lighter color of the final product by 10% to 15% (the lighter the color, the less the thermal migration of the dye) . Therefore, the pre-form has little effect on the thermal migration of dyes.