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Wednesday, January 15, 2014

Notes on Azoic dye

Definition and properties/significance of Azoic Dyes | Why is azoic color called ‘Ice’ and ‘Magic’ color? Also ‘Napthol’ and ‘Pigment’ color? | Description of the general procedure for dyeing cellulosic material | What is Diazotization? | Write down the function of different chemicals used in Napthol Dyeing |Distinguish between Fast Salt and Fast Base |  Explanations of  the stripping method  | Precaution/Remarks is taken while dyeing  |  Trade name and chemical Structure  | Describe the test method of Azoic color

Q. Write down about Azoic Dye?
The dyes containing azo groups – N = N – are called Azoic Dye. These are not ready made dyes but are produced by reaction of two components – Diazocomponent or Base/Salt and coupling component (Napthol). Azoic dye also named as Napthol, Branthol, Magic and Ice color.
Dye formation in fiber occurs on the basis of coupling reaction.

RN2Cl + Rʹ -ONa → R-N=N-Rʹ -OH
Normally two baths are needed for dyeing.
1. Impregnation bath.
2. Developing bath.

Q. Explain the properties/significance of Azoic Dyes.
Ans. Properties/significance of Azoic Dyes:
● These dye stuffs always contain Azo groups in its chemical structure.
● Light fastness property is admirable.
● Brightness of shade is also admirable.
● It is directly insoluble in water.
● These dye stuffs are always used in dyeing cellulosic material.
● Here dyeing operation is completed by two bath arrangement. One is called     impregnation bath and another is called developing bath.
● Alkali resistance is poor to good, Index 2 – 4.
● Suitable for lighter shade dyeing (Light resistance: Poor to very good, Index 2 – 7).
● This dye stuff is called developed dye due to formation of dye in fiber during dyeing process.
●Addition of salt increases the substantivity.
● Napthol dispersed in alcohol, T.R. oil.

Q. Why Azoic Dye is so called?
Ans. This color contains insoluble azo groups in its chemical structure.
– N = N –
Azo group
    That’s why this color is called Azo color.

Q. Why is azoic color called ‘Ice’ and ‘Magic’ color?
 Ans. Ice Color:
          The coupling component is finally soluble in diazotization reaction. Diazotization is a chemical reaction where the  base (Aromatic Amine) is to be converted to a solubilized form by the chemical reaction with NaNO2 at ice temperature (0 – 5˚C).
Why the azoic color is called ice and magic color?
That’s why this dye is called Ice color.
Magic Color:
Two steps are required by dyeing with azoic color. In the first step textile goods are dyed by Napthol color. In the 2nd bath, Base or Salt is used for dyeing. After 2 – 3 minutes dyeing in 2nd bath, the azoic color is seen in the textile goods magically. For this reason this dye is called Magic color. 
Q. Why Azoic dyes are called ‘Napthol’ and ‘Pigment’ color?
Ans. Napthol color:
Azoic coupling components are insoluble in water. To make them soluble in water the textile materials are impregnated in a solution of Napthol and NaOH. As the first coupling component is Napthol color.

          Pigment color:
          Azoic dyes contain Azo group and final color is insoluble in water, so it is called Aoic Pigment.
                                        Base   +     Napthol Azoic dyes
                                     Soluble         Soluble         Insoluble
Q. Describe the general procedure for dyeing cellulosic material with Azoic Dyes.
Ans. General Procedure for dyeing cellulosic material with Azoic Dyes:
           Two bath of individual recipe is used for dyeing with azoic dyes.
1.     Impregnation Bath.
2.     Developing Bath.
Impregnation Bath (1st bath):
Dye Stuff → 3% (According to the wt of the material)
NaOH → 2%
T.R. oil → 2%
Hot water → 3 times
Cold water → 7 times
HCHO → 1.5%
Temperature → 40˚C – 50˚C
Time → For a few minutes (2 – 3)
Developing Bath (2nd bath):

Salt Bath
Fast salt → 6%
Hot water (30˚C – 40˚C) → 2 times
Cold water → 8 times
NaCl → 2% – 3%
Time → 2 – 3 minutes

Base Bath
Fast base → 3%
HCl → 2.5% - 3%
NaNO2 → 1.5%
Cold water → 10 times
Temperature → 0˚C – 5˚C
Time → 15 (2 – 3) minutes
In major cases, we use base bath. It gives very good color in low cost though it is insoluble in water.
Dissolve NaOH in small quantity of hot water with Napthol & T.R. oil in a bath and make a paste. Then add slowly in it, the rest hot water and stir (mix) constantly. After dissolving color perfectly and above mentioned cold water and finally the solution of Napthol is thus obtained, this is cooled to 50˚C if necessary, HCHO may be added in the impregnated bath. Now the bath is ready for steeping textile goods for a few minutes (In this bath, any naptholated goods, excepting the napthol AS – G will look yellow).

In the developing bath salt is dissolved with hot water and then cold water added in the bath. Finally add NaCl in the developing bath. Now treating the above naptholated or impregnated goods for 2 – 3 minutes in this bath. It will be noted that the color will develop the goods magically. Then squeeze the goods and boiling it in a soap bath followed by washing & drying. Now steep the textile goods for a while after developing a bath contains 1.5% of HCl in times of water. It is done only for neutralization of goods. Finally 3% soap and 1.5% soda is taken in a bath containing 15 times and treat the goods for a few minutes and wash the goods in fresh plain water. Then squeeze and dry. In this way, dyeing procedure is completed.

Q. What is Diazotization?
Ans. Diazotization:
          It is a chemical reaction where the fast base is to be converted to a solubilized form by the chemical reaction with NaNO2 at ice temperature (0 – 5˚C).

Diazotization is a chemical reaction where the fast base is to be converted to a solubilized form by the chemical reaction with NaNO2 at ice temperature (0 – 5˚C). 
Q. Write down the function of different chemicals used in Napthol Dyeing.
Ans. Function of different chemicals used in Napthol Dyeing:
Caustic Soda:
à        Soluble the dye material.
à        Produce alkali medium.
T.R. oil:
à        Used as softening agent.
à        Used as dispersing agent.
à        Ensure the actual level dyeing properties.
à        For proper dyeing.
à        To increase the substantivity of the azoic color in textile materials.

Q. Distinguish between Fast Salt and Fast Base
Ans. Comparison between salt and base used in azoic dye:
Fast Salt
Fast Base
1) Fast salts are normally soluble in water.
1) Fast salts are normally insoluble in water.
2) Fast salts reacts diazonium base in its chemical structure.
2) Fast base reacts aromatic amine group in its chemical structure.
3) No extra process required to solobulize the salt.
3) NaNO2 and HCl are required for solobulize the base to produce the diazonium salt.
4) A huge amount of salt is required in developing bath.
4) A little amount of base is required in developing bath.
5) In salt bath additive material is must required.
5) In base bath additive material is not required.
6) Color fixation is poor in case of salt bath.
6) Color fixation is very good in base bath.
7) Fast salt is comparatively costly.
7) Base is comparatively cheaper. 

 Q. Explain the stripping method of Azoic color.
Ans. Stripping method of Azoic color:
NaOH → 4% (According to the wt of the material)
Na2S2O4 → 6%
Lissol Amine – A → 2% (Stripping promoter)
Water → 20 times
Time → 20–30 minutes
Temperature → Up to boiling (100˚C)

Azoic dye stuffs once developed are very difficult to strip. The yellow combination with AS – G and those with napthol of high substantivity are the most difficult one to strip. In order to affect satisfactory stripping Lissol Amine – A is used. It acts as a stripping promoter, when used in conjunction with a reducing agent like sodium hydro-sulphide and alkali.

The dyed material treated in a bath containing Lissol Amine – A, NaOH and sodium hydro – sulphide. 20 times of water of the dyed material is added. Now boil for 20 to 30 minutes until the shade is reduced to a pale (Light) yellow or brown color. The quantity of hydro – sulphide is increased in the case of yellow combination. 

Q. Write down the Precaution/Remarks is taken while dyeing with Azoic Dyes.
 Ans. Precaution/Remarks are taken while dyeing with Azoic Dyes:
                   i. Impregnation bath liquor can be preserved for a day or two days.
                ii. Developing bath liquor cannot be preserved for a day.
               iii. Naptholation material should never allow to come in contact with acid, alum and sunray.
               iv. Generally 2 – 3 minutes duration is suitable for both impregnation and developing bath.
                 v. If any way impregnating and developing liquor mixed together, the entire nature will be inactive and useless.
               vi.  During dyeing of protein fiber (Silk, Wool) with azoic dye, we should be very careful not to damage the protein fiber due to high alkali concentration.
                vii. Bases yield comparatively better performance than salt.

Q. Write down five Trade name of Azoic color.
Trade Name
Ciba Naphol
Igra Napthol
Nacco – thol

Q. Show the chemical Structure of Azoic Dye.
Ans. Chemical Structure of Azoic Dye:

The chemical Structure of Azoic Dye.
Q. Describe the test method of Azoic color.

Ans. Test method:
           Take a sample dyed or printed with azoic color in a test tube in the presence of a reducing agent named Sodium Hydro/Bisulphide water liquor. Now treat the sample up to boiling stage. Then we will observe the color will come out completely from that sample. Now this liquor and sample are to come in an oxidizing action in the presence of air or an oxidizing agent. If the color is not received to it, then it will indicate that the sample are dyed or printed with azoic color.

        i. All the chemicals according to the recipe are mixed with water to make a suitable solution.
     ii. At definite temperature (0˚C–5˚C), if the material treated with this for 15 to 20 minutes then light brown color will be arise. This is known as diazotization.
   iii. To remove excess HCl we should use Na – Acetate.
To protect from sunlight, we can use Al – sulphate.]

                                                       Credits goes to- Fazle Bari Ranga
                                                                   PTEC- 5th Batch

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About the Author :

He is Md. Abu Sayed from Naogaon, Bangladesh. He is a Textile Engineer and working as a Testing Engineer at Bureau Veritas CPS (BD) Ltd. He also Likes article writing on Textile and Clothing Technology.

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