Disperse dyes

Disperse dyes is a class of non-ionic dye, which has low water solubility and exists in water primarily in a highly dispersed state by means of the effect of the dispersing agent in the process of dyeing. It is mainly used for dyeing polyester fibers. The chemical structure of most disperse dyes belong to monoazo type, which accounts for about 80% of all the disperse dyes. And then , anthraquinone accounts for  about 15%, and other types of structures about 5%. It is enerally believed that the dyeing mechanism of disperse dye in water is : In dyeing temperature, part of the disperse dyes dissolves into dye molecules in the dye bath by means of the effect of the dispersing agent, and then is adsorbed on the fiber surface in the form of the molecule. At the same time, the amorphous region in poly ester fiber expands to form a hole, which is large enough to accommodate the dye molecules in dyeing temperature. So it is easy to make the dye molecules diffuse in the fiber, and at the end of staining, the previously puffed hole shrinks as the temperature decreases and makes the dye molecules encased within the fiber, so that the dye molecules can eventually form a single molecule or low molecular weight aggregates to be encased within the solid fiber. Foreign scholars believed that the crystal form of disperse dyes (ie, crystalline) impacts its dyeing performance, but the results later denied this claim. However, if the crystalline form of the  disperse dyes is different, its lattice energy also will be different. So the crystalline form of the disperse dyes affects their commercialization process.

Disperse dyes can be divided into five series:
(1) E-type disperse dyes : they have good leveling properties, and are suitable for dip dyeing process. Besides, some can be used for thermal transfer printing process.
(2) SE-type disperse dyes: they have general leveling properties and good color fastness to sublimation, and can be used in  the dip dyeing and pad-dry-cure dyeing process of the polyester fibers.
(3) S-type disperse dyes: they have high color fastness to sublimation, and are mainly used in the pad-dry-cure dyeing process of the polyester blended fabric.
(4) P-type disperse dyes: they are used for the anti discharge printing of the polyester fibers and cellulose fibers blended fabric.
(5) RD-type disperse dyes: they can be used for the rapid dyeing of the polyester fibers. According to the different molecular structure of the disperse dyes , they can be distribute into azo, anthraquinone, nitrodiphenylamine ,heterocyclic ring and other types. Because of the absence of water-soluble gene, the  disperse dyes dissolved in water is minimal.

Disperse dyes are commonly used to dye in two ways, namely high temperature and pressure method and the hot-melt method. The so-called high temperature and pressure method is actually that the temperature is only 130 ℃, and the pressure is only 0.2MPa (gauge pressure). It was so called because other dyes are usually conducted at atmospheric pressure, and the dyeing temperature generally does not exceed 100 ℃. The pad-dry-cure dyeing is always not carried out in water. On the contrary, the dye staining solution should be padded on the surface of the fiber, and then the dried fiber is fed to the 180 ~ 220 ℃ drying room for 30s. In this process ,the dyes sublime to leave the fiber colored. According to this dyeing process, the disperse dyes can be divided into high, medium and low temperature type. And the high-temperature type disperse dyes have the largest molecular weight and the best resistant sublimation fastness.

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