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Azoic dyeing procedure

Dyeing Procedure

The azoic dyeing process can be done in four stages for better outcomes.

(A) Naphtholation
(B) Naphtholation of material
(C) Preparation of Diazotised base
(D) After treatment

Azoic dyed fabric
Azoic dyed fabric

Explanation -

(A) Preparation of the Naphthol solution:(Naphtholation) 

Two methods of dissolution of Naphthol -
(i) Hot dissolution method

In this procedure, a protective colloid, like alizarine red Oil, is carefully pasted onto the naphthol, and a little amount of quandary is added to forestall lump formation. 

The paste is then combined with the mandatory amount of boiling water. 

Next, heat is applied to bring the naphthol suspension to a boil. 

Tire hot naphthol dispersion is mixed with the required quantity of sodium hydroxide. 

When hydroxide is added, naphthol is modified into its sodium component, which dissolves in predicament to produce a transparent solution. 

If the answer isn't clear, it's boiled for some more minutes till it becomes clear. within the case of naphthols AS-TR, AS-BR, AS-SW, AS-GR, AS-SG, AS-SR the naphthol is pasted with the desired amount of Turkey red Oil and hydrated oxide. 

The paste is warmed then the naphthol is dissolved by the addition of boiling water.

The resulting solution is further boiled, if necessary, to urge a transparent solution.

(ii) Cold Dissolution method

The "cold dissolving method" is one that doesn't involve heating the answer. 

The naphthol is pasted with the required amount of denatured alcohol in this way, and therefore the necessary amount of hydroxide solution is then added to that. 

The naphtholate is instantly formed, and full disintegration is induced by the addition of a tiny low amount of soppy water. 

This process is speedier and also makes it possible to make solutions with incredibly high concentrations.

(B) Naphtholation of Material: 

The material is thoroughly scrubbed (and either consistently dry or wet), and it works well within the naphthol bath. 

At temperature, the treatment is sustained for 15 to twenty minutes. In rare circumstances, adding common salt enhances naphthol absorption. 

within the presence of common salt, naphthols like AS-G, AS-SG, AS-GR, etc. are added.
The uniformly compressed and naphthalized substance must not be handled with wet hands or up-to-date with any metals apart from stainless steel. 

Additionally, the fabric has to be grown quickly and should not be exposed to direct sunlight.

(C) Preparation of the Diazotised base (developing bath): 

Primary aromatic amines, which fast bases are, will be diazotized using acid. the 2 commercially available varieties of the diazo components are free amines and fast salts. 

The titles given to commercial goods are deceptive because the colour relies on the coupling element, for instance. Sometimes a red colour might not be produced by a quick Red B base. Except for the Fast Yellow GC base, which generates a yellow colour when 

combined with Naphthol AS-G, the colours mentioned within the product's commercial names are typically applied when the merchandise is combined with Naphthol AS. 

Multi-stage diazotization is best-drained wooden vessels and involves a variety of steps. 

Water cannot dissolve fast bases. Though the solubility varies noticeably, their hydrochlorides are soluble. the subsequent processes are involved in diazotization, which is the creation of a radical by a chemical process with acid. 

The free base is transformed into water-soluble hydrochloride: this can be accomplished by the bottom being exposed to strong acid at an extreme temperature. 

At temperatures as low as 5 to 8°C, or even perhaps 0°C, acid is employed to treat the soluble hydrochloride of the base. 

To accomplish this, nitrite is added to an answer of base hydrochloride in excess acid. 

The diazotization reaction is symbolically represente
The diazotization reaction is symbolically represented

The resulting diazonium chloride is unstable even at ambient temperature and decomposes when nitrogen is released. Diazotization is performed using one of two main procedures called direct or indirect approaches. 

(D) After treatment: 

When azoic dyes are applied to cotton, fast bases and soluble naphthols are wont to create an insoluble pigment in an aqueous phase. because of this, there's a risk that the pigment will form within the bath itself and deposit on the surface of the substance being treated. 

Poor fastness properties are caused by the deposition, but it also prevents the important shade from developing. To accomplish the subsequent goals, soaking is consequently required as a part of the after-treatment. 

(1) Eliminating mechanically retained pigment will significantly increase the quality of rubbing fastness. 

(2) Some combinations of naphthol and base exhibit noticeable tone shifts. True colours are produced with the employment of soaping.
(3) Soaping also shows significant improvements in the degree of fastness particularly to light and chlorine. 

The majority of the naphthol-base mixtures will be washed at the boil using 3 g/l soap and 1 g/l sal soda for 20 to half-hour, followed by a hot-water and cold-water rinse. 

However, some combinations significantly lose depth without improving in terms of fastness qualities. the subsequent combinations are soap-soaked at 60-65°C. 

Questions -

  1. What are the different stages of the azoic dyeing process?
  2. Explain the Naphtholation process of azoic dyeing.
  3. Explain the Naphtholation of material for azoic dyeing.
  4. Explain the Preparation of Diazotised base of azoic dyeing.
  5. Explain the After treatment process of azoic dyeing.


Definition of AZOIC DYE. (n.d.). from

Dyeing of cotton fabric with azoic dyes. (2020, April 25). Textile Study Center.

Patwary, E. M. Z. (2012, April 25). What is azoic dye. Textile Fashion Study; Engr. Mohammad Zillane Patwary.

Sayed, A. (n.d.). An overview of Azo dyes. from

Textile Knowledge. (n.d.). from

Yamaguchi, Y. (1956). Azoic Dyes. Journal of Synthetic Organic Chemistry Japan14(4), 239–245.

Continue read,

Part 1 Introduction of azoic dye

Part 2 Azoic dyeing procedure

Part 3 Azoic dye- process, properties and blinding of colours

Writer - Rushikesh Patil (Textile Engineer)
(DKTE Society textile engineering college ichalkaranji)
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