Disperse dyes are one of the major classes of dye that are non-ionic in nature and having substantivity for hydrophobic fibers especially polyester, nylon etc. They are insoluble in water at room temperature and slightly soluble only at higher temperature. Disperse dyes have overall good to excellent light and wet fastness properties. Diffusion number of Disperse dye is measured with polyester fiber.
As their name implies, these dyes are present in the dye bath as a fine aqueous suspension in the presence of a dispersing agent. These dyes contain micro-fine dye particles with a diameter below 1 µm as well as varying amount of dispersing agent. Disperse dye dispersion is carried out with dispersing agent. The water dissolves a small amount of the dye in monomolecular form. The hydrophobic fibers then absorb the dye from the solution. Because these dyes are non-ionic organic compounds of relatively low molecular weight, many sublime on heating and dyeing by absorption of the dye vapor is also possible.
Their major use today is for the coloration of polyesters, the most important group of synthetic fibers.
Fig: Examples of Disperse dye
Fig: Partial chemical structure of lignosulphonate & alkylsulphonate and dispersing agent
Properties of Disperse dye:
- Disperse dyes are not soluble in water.
- For dyeing with disperse dye, dispersing agent is a must.
- This is an organic substance that is free from ionizing group.
- Overall light and wet fastness is good to excellent.
- Acidic medium is used for the application of disperse dye. In strong alkaline medium, some azo disperse dye undergoes degradation and thus decreases the percent exhaustion.
- These dyes are highly used for synthetic fiber dyeing like polyester, nylon, tri-acetate, di-acetate etc.
- These dyes exhibit smaller molecular size than the other dyes.
- Dyeing with disperse dye is carried out in high temperature. As, these dyes are mostly insoluble in water but have limited solubility only at higher temperature.
- These are derivatives of azo, anthraquinone, nitro and quinine groups.
- Melting temperature of this dye is 122-150℃ and they are in crystalline, powder and paste form.
- Variety shades of color is possible.
- On the application of heat, color will be fade.
Trade names or commercial names of Disperse dye:
Diffusion number of Disperse dye:
A polyester film is wrapped around a glass rod and dyed with disperse dyes under simulated conditions. At the end of dyeing the number of layers dyed is counted and designed as diffusion number of the dye. These number provide a basis of selection of dyes for producing combination shades.
Disperse dyes are an important dye class for hydrophobic fibers. Nowadays, the popularity for synthetic fibers like polyester increases the popularity of Disperse dye also. In our industry, polyester is now widely dyed with disperse dye.
Know more about Cationic dye able Polyester.