Definition | Dye History of Disperse Dye | Properties of Disperse Dyes

The term disperse dye have been applied to organic coloring substance which are free from ionizing groups. They are of low water solubility and are suitable for dyeing hydrophobic fibers.

Disperse dyes are the only water insoluble dyes dyeing polyester and acetate fibers. Disperse dye molecules are the smallest dye molecules among all the dyes[citation needed]. A disperse dye molecule is based on an azobenzene (Disperse Red 1) or anthraquinone amine (Disperse Orange 37) molecule with, amine, hydroxyl, etc. groups attached to it.

They tend to be fairly hydrophobic (though this depends on the structure of R and R2) but not as a long hydrocarbon because the -COOC- groups cause some polarity. The polymer chains in a sample of polyester are highly crystalline and quite tightly packed together. The result of this is that polyesters have very little affinity for large ionic dyes- the dyes form satisfactory inter-molecular interactions. Therefore, acid and direct dye classes are useless for this polymer.

Disperse dyes have low solubility in water, but they can interact with the polyester chains by forming dispersed particles. Their main use is the dyeing of polyesters, acetates and polyamides. The general structure of disperse dyes is small, planar and non-ionic, with attached polar functional group like -NO2- and -CN. The shape makes it easier for the dye to slide between the tightly-packed polymer chains, and the polar groups improve the water solubility and affect the color of the dye.

The dye is generally applied under pressure at temperatures of about 1300C. At this temperature, thermal agitation causes the polymer's structure to become looser and less crystalline, opening gaps for the dye molecules to enter. The interactions between dye and polymer are thought to be Van-der-Waals and dipole forces.

History of Disperse dyes

In 1922, Green and Saunders made one type of colored azo compound, in which a solubilizing group (for example- methyl sulphate, -CH2-SO3H) is attached to amino group. In dye bath, they are slowly hydrolyzed and produce azo compound and formaldehyde bi sulphate. This free azo compound was capable of dyeing cellulose acetate fibers. This dye was named “ionamine”. But this ion amine did not give satisfactory result in dyeing.

Later in 1924, Baddiley and Ellis produced sulpho ricinoleic acid (SRA) for dyeing acetate fibres. This SRA was used as dispersing agent. Later it was seen that SRA was capable of dyeing Nylon, polyester, acrylic etc. In 1953 this dye was named as “Disperse Dye”.

Properties of disperse dye

1. Disperse dyes are non-ionic dye
2. They are ready made dyes
3. They are slightly insoluble in water
4. They have substantivity for one more hydrophobic fiber like cellulose acetate, nylon, polyester
5. Carrier and dispersing agents are used for dyeing
6. They have fair to good light fastness with rating about 4-5
7. Wash fastness of disperse dye is moderate to good with rating about 3-4
8. It has smaller molecular size
9. They don’t undergo any chemical change during dyeing