Name of the experiment:
Printing of cotton fabric with Azoic dyes.
- To print a material practically.
- To observe the practical advantages and disadvantages of this dye.
- To compare the theoretical idea with practical experiment.
Azoic dyes are not ready-made dyes but are produced by reaction of two components-Diazocomponent or Base/Salt and Coupling component (Naphthol). Azoic colors give wide range from yellows, orange, scarlet, red, blues, blacks, but there are only few greens. Also called Naphthol Dyeing, is recommended to get the bright and fast shades in maximum depth similar to vat dyeing. Lemon yellow, dark orange, blood red, pink, red -orange, red brown, yellow brown, tan, dark red, violet, brown violet, coffee-violet, bright blue, china blue, navy blue, blue-black and royal blue are dyed successfully under this style.
Dye formation in fiber occurs on the basis of coupling reaction.
RN2Cl + R/-ONa → R-N=N-R/-OH
The colored substance formed Azoic dye from these essentially colorless 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-
Naphthols are insoluble in water and converted into soluble form by treating with alkali. The fabric is in pregnated with β-naphthol and NaOH Solution and converted into β-Naphthol Na-β-Naphtholate.
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-5o
The impregnated material 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.
- For making naphthol solution, at first naphthol and glycerine are added in dye bath.
- Then NaOH is added into the bath.
- Finally salt and water are added into the bath.
- Then fabric is immersed into this solution for few minutes. And the fabric becomes naphthaled.
For base recipe:
- At first required amount of base, HCl, NaNO2 are mixed another dye bath at 00-50C (with ice).
- Then acetic acid and sodium acetate are added into the dye bath. And mixed them very well.
- Finally thickener and required amount of water is added and stirred them very well for getting required viscosity.
Block printing method:
- The fabric which will be printed is placed on the printing table.
- The printing paste is put on the tray box.
- The block is selected and it is touched with print paste.
- Then block is pressed upon the sample fabric.
- After pressing the block on the sample fabric the block is put off from the fabric.
- Finally we get the printed fabric of required dyes.
- Soap wash with 0.5 g/L detergent
- Cold wash.
Printing of cotton fabric with azoic dyes has excellent build up property and maximum fixation. Shade is also bright. By this experiment we have acquire knowledge about process of printing cotton fabric with azoic dyes in combination shade. The shade of printed fabric is moderately good, as we required. Special thanks to our teacher and his assistants for grate cooperation.
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