Printing of Cotton Fabric with Azoic Dyes | Printing Process of Cotton Fiber with Azoic Dyes

Introduction:

Azoic dyes are not ready-made dyes but are produced by reaction of two components-Diazocomponent or Base/Salt and Coupling component (Naphthol).

Dye formation in Fibre occurs on the basis of coupling reaction.

RN2Cl + R/-ONa ® R-N=N-R/-OH

Azoic dye

The coloured substance formed Azoic dye from these essentially colourless compound is insoluble in water and the washing fastness of the shade is excellent.

Chemistry of dyeing:

Dyeing process of azoic dyes includes three main stages. They are-

I) Naphtholation
II) Diazotisation
III) Coupling.

I). Naphtholation: Naphthols are insoluble in water and converted into soluble form by treating with alkali. The fabric is in pregnated with b-naphthol and NaOH Soln and converted into b-Naphthol Na-b-Naphtholate.  
II) Diazotisation: A base containing amino group reacts with sodium nitrite to a soln of the hydro chloride of the base in the presence of excess of HCl at 0o-5oC.

III) Coupling: The impregnated mtl is treated in a bath containing diazonium soln to carry out coupling and azoic colour is produced.

Style of printing:

Direct style.

Method of printing:
Block & Screen printing method.

Procedure:

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:

Block printing method: