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-

Naphtholation
Diazotisation
Coupling

(1). Naphtholation : Naphthols are insoluble in water and converted into soluble form by treating with alkali. The fabric is in pregnated with ß-naphthol and NaOH Solⁿ and converted into ß-Naphthol Na-ß-Naphtholate.

(2) 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 0^o-5^o

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

Process Sequence For dyeing with Azoic dyes:

Textile mtl is prepared

↓

Fabric/textile mtl is treated with Naphthol Solⁿ

↓

Preparation of base salt solⁿ

↓

Naphthol treated fabric is treated with

↓

Diazo-solution

↓

Colour developed

Recipe:

*For Naphtolation:*		*For Base solution:*
Napthol	5% owf	Base	5% owf
Glycerine	2% “	HCl	3% “
Caustic soda	6% “	NaNO2	2% “
Common salt	15% “	CH3COONa	15% “
Temperature	Room temp.	Acetic acid	0.5% “
Time	20-30 min	Temperature	0-5^O C
M:L	1:20	Time	20 min
		M:L	1:20

Calculation:

For Naptholation	For Base Solution
Caustic Soda = 0.6 gm	Base = 0.5 gm
Common Salt = 1.5 gm	HCL = 0.3 gm
Napthol =0.5 gm	NaNO2 = 0.2 gm
Glycerine = 0.2 gm	CH3COONa = 1.5 gm
Water= 200 ml

Description of the process:

Naphthol preparation:

The required amount of alkali and common salt was taken to a bath.
The Naphthol and Glycerine are taken in a bath and stir it until dissolve.
Then the above two liquor are added in a bath with the required water.
The fabric of required weight is taken and impregnated in the naphthol solution and squeeze it until dry otherwise premature reaction may occur.

Base colour preparation:

The required amount of base color, HCl, acetic acid, Na acetate, are added in a bath.
Then add the required amount water (at 0-5°C) to make the liquor.
Finally add the required amount of NaNO₂ to complete the diazotisation.

Development:

Then the squeezed fabrics are mixed in the bath of base colour one by one and within 2-3 minute the magic color is obtained.

After treatment:

Cold wash.
Hot wash.
H₂O₂ (3 g/L) at
Acid wash (1-2 g/L) at room temperature.
Hot wash.
Cold wash.
Drying.

Remark:

The sample of the dyed material seems to have correct shade and it shows good fastness especially wash fastness. So it is proved that maintaining proper temperature and time does the experiment.

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