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Azoic Dye & dyeing or coloration process of fabric with Azo dye -2 (Last Part)

Azoic Dye & dyeing process of fabric with Azo dye


Azoic Coupling


Most of the azoic coupling components are arylides of beta-oxynaphthoic acid (BON) also referred as Brenthols.

Any azoic coupling component can be combined with any diazotized base ,so that 30 different Naphtholand 50 bases,can yield 1500 possible combinations.




Naphthols differ widely from one another in their affinity or substantivity for cotton fibre. They can be classified as:


1) Low substantivity Naphthol

azoic dyeing

2)Medium substantivity Naphthol

azo dye, dyeing

3) Higher substantivity Naphthol

azo dye, dyeing


4) Still higher substantivity Naphthol

  • Substantivity of Naphthol can further be increased by adding electrolyte like common salt or glauber’s salt.



Subtantivity of Naphthols


  • With high substantivity of Naphthol, only small residue of this product will remain unutilized in the bath after application
  • With low, medium and moderate substantivity naphthols usually salt is added to increase their substantivity

Method of dissolution of naphthols


There are two method : Hot and Cold

  • In the hot method,the naphthol is pasted with turkey oil,the required amount of NaOH solution is added and boiling water is poured.
  • In the cold dissolving, the naphthol is stirred with required amount of methylated spirit,sodium hydroxide used is less than that in Hot process,cold water is added to get clear solution.

Use of caustic soda


  • Azoic coupling components are insoluble in water and have to be converted into their alkali salts to dissolve them. Usually caustic soda solution is used for the purpose.
  • The two acidic hydrogen can be replaced sodium.


High degree of brightness


  • 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.
  • Azoicdyes are used for producing bright shade of color such as orange, red,scarlet, navy blue and black color.

Flow chart or Process Sequence for dyeing with Azoic dyes:


                     Textile material is prepared


                    Fabric/Textile material is treated

                        with Naphthol Solution


                Preperation of base salt solution


              Naphthol treated fabric is treated with

                            Diazo – solution


                           Color developed


                              After Treatment




Typical procedure of Azoic Dyeing or Printing:

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 0‐50C (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.



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


After treatment :

After printing the printed fabric is dried at 100‐105 for 5‐10 minute in a dryer.If the naphtholation process is not so sufficient. Then the printing becomes uneven.


How does Azo dye make in labratory


A crystallizing dish is half filled with ice. Four beakers containing the following solutions are placed in a ice bath:


Beaker 1:   50 mL of an acidic solution of sulfanilic acid

Beaker 2:   10 mL of an aqueous solution of sodium nitrite

Beaker 3:   50 mL of an acidic solution of 1‐naphthylamine

Beaker 4:   50 mL of an alkaline solution of 1‐naphthol


The sulfanilic acid solution is mixed with the aqueous solution of sodium nitrite while stirring. Equal volumes of the mixture are poured into the beakers 3 and 4.Then Azo dye will be prepared.


Testing method of Azo dye



A sample which is dyed with azoic dye is taken in a test tube.Then we add reducing agen Sodium Hydro or Bisulphide water liquor.After that we should boil the test tube.We will observe the color that will come out from the sample completely.Then the liquor and sample creat an oxidizing reaction with the presence of air or an oxidizing agent.If the color does not received that means the sample are dyed with azoic dye


Difference between azoic dye and azo dye


                         Azoic dye                     Azo dye
1. Azoic dye is Insoluble Azo  group1.  Azo dye is Soluble Azo group
2. Azoic dye is insoluble in water2. Azo dye is Soluble in water
3. It not found in the ready made dye3. Azo dye is found in the ready made dye
4. Azoic dyes need of diazotization and coupling4. No need
5. Azoic dye Application is compound5. Application is simple
6. Azoic dye is Less used6. Azo dye is Widely used
7. Two bath process7. One bath process
8. Azoic dye is Comparatively costly8. Azo dye is Cheap



Hazardous nature of azo dyes

Certain azo dyes can break down under reductive conditions to release any of a group of defined aromatic amines. Consumer goods which contain listed aromatic amines originating from azo dyes were prohibited from manufacture and sale in European Union countries after the German ban in 1997.  Many azo pigments are non‐toxic, although some, such as dinitroaniline orange, ortho nitroaniline orange, or pigment orange 1, 2, and 5 have been found to be mutagenic. Likewise, several case studies have linked azo pigments with basal cell carcinoma.

Azoic Dye & dyeing or coloration process of fabric with Azo dye -1

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