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. 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 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:

Disperse dyes are nonionic dyes. So they are free from ionizing group.
They are ready made dyes and are insoluble in water or have very low water solubility.
They are organic colouring substances which are suitable for dyeing hydrophobic fibres.
Disperse dyes are used for dyeing man made cellulose ester and synthetic fibres specially acetate and polyester fibres and sometimes nylon and acrylic fibres.
Carrier or dispersing agents are required for dyeing with disperse dyes.
Disperse dyes have fair to good light fastness with rating about 4-5.

Classification of Disperse Dyes:

According to Chemical Structure:

Nitro Dyes
Amino Ketone dyes
Anthraquinonoid dyes
Mono azo dyes
Di- azo dyes

Recipe:

Disperse Dyes	4 parts
Dispersing agent	2 parts
Water	As required
Thickener	83 parts
(NH₄)₂SO₄	0.7 gm
NaClO₃	0.2 gm

Print paste preparation:

Thickener paste preparation (70 gm sodium alginate + 13 C.C H₂O stirr with heat)
4 gm dyes + 2 gm dispersing agent
7 gm (NH₄)₂SO₄ + 0.2 gm NaClO₃
(1 + 2 + 3) Stirr uniformly

After treatment:

The printed fabric is steamed in the steamer 10 min at 105 – 110 ⁰C to penetrate the dye in the fabric and fix it.

Comments:

Disperse dyes have low molecular weight (200 – 400 gm per mole) and are non ionic which is necessary for preparing stable dispersions. The fact that disperse dye stuffs must be able to prepare in free divided states is important. To achieve level dyeing the particle size also must be maintained below 4 microns and preferably 0.5 – 3 microns. Naturally the particle size also must be as uniform as possible. Since disperse dye stuffs are crystalline in the pure state it is frequently difficult to grind them to meet the above requirements. Dye particles of over 4 microns produce specky coloration.

Some of the disadvantages of disperse dyes included limited wash fastness, gas fading, the resistance of multi step fibre pretreatment, the problem of flocculation of the dye stuff, the addition cost of the required additives and the environmental concern over many of the aromatic solvent dye carries employed. Barre effects do occur but can be controlled by standing the dyeing cycle and slightly increasing the dye bath temperature.

From this experiment we can get a clear idea about Disperse dyes. From others dye this type of dye is different. During this experiment we have to face some problems that are to be considerable. Overall, the knowledge of this dye helps us to dye Man made fibre especially Polyester properly and helps us in our practical life.

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