Dyeing of Cotton Fabric with Azoic Dyes | Dyeing Process o Cotton Goods with Azoic Dyes

Name of the experiment: Dyeing of cotton fabric with azoic dyes.

The dyes containing insoluble azo group (-N=N-) are known as azoic dyes.

These dyes are not found in readymade form. Azoic dyes are produced by a reaction between two components. The components are:

1. Coupling Compound ( Naphthol)
2. Di-azo –compound or diazo base or diazo salt.

The colored substance formed from this colorless compound is insoluble in water and washing fastness of this shade is excellent.

Reaction of
Azoic Dye:

Naphthols are insoluble in water and they are converted into water soluble compound by treating with alkali.

A base containing amino group (-NH2) reacts with the NaNO2 (Sodium Nitrite) to form a solution of diazonium chloride of that base in presence of excess HCl at 00-50C temperature.

Coupling/ Developing:
The impregnated material is treated in a bath containing diazonium solution to carry out to coupling and thus color is produced inside the fabric. The PH maintaining is important.

Recipe of Azoic Dye:


Naphthol = 1.3gm
Glycerine = 1.5gm
Caustic soda = 2 gm
Common salt = 2 gm
Water = 94 cc.
Time = 20 minute.
Temperature = room. 

For diazotization):

Base color = 1.5 gm
HCl = 1.4 ml
NaNO2 = 0.6 gm
Acetic acid = 0.8 gm
Sodium acetate = 1.2 gm
Water = as required to make 100 gm paste
Temperature = 00-50C (with ice)


For naphtholation:
1) For making naphthol solution, at first naphthol and glycerine are added in dye bath.
2) Then NaOH is added into the bath.
3) Finally salt and water are added into the bath.
4) Then fabric is immersed into this solution for few minutes. And the fabric becomes naphthaled.

For base recipe:
1) At first required amount of base, HCl, NaNO2 are mixed another dye bath at 00-50C (with ice).
2) Then acetic acid and sodium acetate are added into the dye bath. And mixed them very well.
3) Finally thickener and required amount of water is added and stirred them very well for getting required viscosity.

Printing process:

The naphtholated fabric is then printed with base printing paste by block and screen printing method.

After treatment:

After printing the printed fabric is dried at 100-1050 for 5-10 minute in a dryer.

Our naphtholation process was not so sufficient. So printing becomes uneven. But we learn about the printing of cotton fabric with azoic dye.

Because of high degree of brightness, ease of application and excellent fastness properties (except rubbing fastness which can be improved by using certain auxiliaries) azoic combinations (naphthol and bases) are widely used in printing on cellulose fiber fabrics. Azoic dyes are used for producing bright shade of color such as orange, red, scarlet, navy blue, and black color. By this practical we acquire knowledge about the printing process of cotton fabric with azoic dyes. This practical will help us in our study life as well as job life. Especial thanks to our teacher and his assistants for great co-operation. 


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Anonymous said...

why are azoic dyes limited in the range of shades?

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