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

Sunday, May 20, 2012

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

Dyes are colored, unsaturated organic chemical compounds capable of giving colour to a substrate (a textile), i.e. colouring or dyeing it.

The term “disperse dye” have been applied to the organic colouring substances which are free from ionizing groups, are of low water solubility and are suitable for dyeing hydrophobic fibres. The dye has derived its name for its insoluble aqueous properties and the need to apply it from an aqueous dispersion. Of all the dyes, they are of the smallest molecular size.

Disperse dyes have substantivity for one or more hydrophobic fibres e.g. cellulose acetate, nylon, polyester, acrylic and other synthetic fibres.

The negative charge on the surface of hydrophobic fibres like polyester can not be reduced by any means, so non-ionic dyes like disperse dyes are used which are not influenced by that surface charge.

History of Disperse Dye

In 1922, Green and Saunders made one type of coloured 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 fibres. 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 Dyes

Ø Disperse dyes are nonionic dyes. So they are free from ionizing group.
Ø They are ready made dyes and are insoluble in water or have very low water solubility.
Ø They are organic colouring substances which are suitable for dyeing hydrophobic fibres.
Ø Disperse dyes are used for dyeing man made cellulose ester and synthetic fibres specially acetate and polyester fibres and sometimes nylon and acrylic fibres.
Ø Carrier or dispersing agents are required for dyeing with disperse dyes.
Ø Disperse dyes have fair to good light fastness with rating about 4-5.
Ø The wash fastness of these dyes is moderate to good with rating about 3-4.
Ø Of all dyestuffs disperse dyes are of smallest molecular size.
Ø Generally disperse dyes are derivatives of azo, anthroquinone, nitro and quinine groups.
Ø They do not undergo any chemical change during dyeing.
Ø In presence of nitrous oxide, textile materials dyed with certain blue and violet disperse dyes with an anthraquinone structure will fade. This is called gas fading of disperse dyes which is a defect of this dye.

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Sunday, May 20, 2012