Dyes are unsaturated colored organic chemicals capable of giving color to a substrate (a textile), ie dye or dye. The term "dispersed dye" has been applied to organic coloring substances which are free of ionizing groups, are of low solubility in water and are suitable for dyeing hydrophobic fibers. The dispersed dyes have substantivity for one or more hydrophobic fibers, e.g. cellulose acetate, nylon, polyester, acrylic and other synthetic fibers.
The negative charge on the surface of the hydrophobic fibers such as the polyester can not be reduced in any way, whereby nonionic dyes are used as dispersed dyes which are not influenced by that surface charge.
In 1922, Green and Saunders fabricated a type of colored azo compound, in which a solubilizing group (eg, methyl sulfate, -CH2-SO3H) is attached to the amino group. In the dyebath, they are slowly hydrolyzed and an azo compound and bi-sulfate formaldehyde are produced. This free azo compound was capable of having cellulose acetate fibers. This dye was called "ionamine". But this ionic amine did not give satisfactory results in the tissue.
Later, in 1924, Baddiley and Ellis produced sulfo ricinoleic acid (SRA) to stain the acetate fibers. This SRA was used as a dispersing agent. Later it was seen that SRA was able to dye Nylon, polyester, acrylic, etc. In 1953 this dye was named as "Disperse Dye".