Common Problems & Corrective Action in Azoic Dyeing. Common Problems Of Azoic Dyeing

1. GREEN UNIVERSITY OF BANGLADESH
Department Of Textile
ASSIGNMENT
Remarks:
Course Code : TE 305
Course Title : Textile Coloration II
Submitted By:
Name : Md Rakibul Hassan
ID : 183014057
Section : E1
Department : Textile
Date Of Submission : 13-09-2020
Assignment On : Explain the Common Problems and Corrective Action
in Azoic Dyeing.
Submitted to:
Name : Mr. Md Mahbubur Rahman
Designation : Senior Lecturer
Department : Textile

2. Explaining the Common Problems and Corrective Action in Azoic Dyeing
Introduction:
Azoic dye is that which has insoluble azo group. Azoic dyes do not get in ready-made form in the
market. It is produced by reacting two components named coupling method and diazo component. It
should be noted here that, azoic dye is different from other dye and the application process also
different from others. It also called ice color or magic color because it needs very low temperature.
The insoluble azoic colors are synthesized inside the fiber by coupling of two individual components
neither of which is a dye itself. These two components are on aromatic diezoniem solt and an aromatic
hydroxyl compound. After diazotization the actual color is developed in the substrate. In application
of azoic colors, the first step is selecting the west suitable diazo and coupling components
combination of a particular purpose is to decide which of the napthols can be used in conjunction
with the available diazo components to give the color closest to the chemical shade and depth.
Dye formation in fibre occurs on the basis of coupling reaction.
RN2Cl + R-ONa R- N=N-R-OH,
Azoic dye
Some Different Name of Azoic Dye:
1. (Icecolor) - The coupling component which is finally soluble in diazotization reaction the ice
water (0˚C- 5˚C) required to the process so it is called ice color.
2. Magic color
3. Naphthol color
4. Pigment color
Properties of Azoic Dyes:
1. This type of dye is mostly used for lighter shade dyeing.
2. It is directly insoluble in water.
3. Insoluble azo group present in it.
4. Brightness of azoic dye is good.
5. Addition of salt increases substantively.
6. High fastness characteristics of this dyestuff admirable.
7. Brightness of shade is also admirable.
8. Dyeing operation is completed by two bath arrangement such as developing bath and
impregnating bath.
9. This dyestuff always contains azo groups in its chemical structure.
10. Dyestuff always used in cellulosic materials.
11. Wash fastness is very good here.
12. Napthol dispersed in alcohol T.R.O.
13. Coupling is necessary for color production.
14. In alkaline solution, coupling is done.
15. It is mainly applicable for cellulose fibres.
16. Application time has needed more here.
17. Azoic dye is comparatively cheap than other dyes.
18. Dyeing process is done by using three processes here such as coupling, naptholation and
diazotization.

3. 19. Here, final color is produced within few seconds after immersing the next materials in the dye
solution.
20. It is perfect for small scale industry.
21. It is used for coloring small amount of textile materials dyeing.
22. Azoic dye is not popular as reactive dye or disperses dye.
23. Cellulose cotton but also jute, nylon, polyester, hemp, acetate, rayon, linen are dyeing by azoic
dyes.
24. Insoluble azo group present in it.
25. It is dercetly insoluble in water.
26. Color is formed from solubilesed component but the ultimate colored product in always insoluble.
27. Alkali resistance: poor to good
28. Light resistance: poor to good
29. Wash fastness: very good
30. Brightness of azoic dye is good
31. This dye is called developed dye due formation of dye in fabric during dyeing process.
32. Addition of salt increases substantivity.
Common Problems and Corrective Action in Azoic Dyeing:
There are some problems that happen in azoic dyeing. Lets have a discussion about the problems and
corrective action in azoic dyeing. Some common problems and corrective action are given-
1. Uneven Shade
2. Naphthol Migration
3. Slow Coupling Reaction
4. Afinity of Base Towards Cellulose
5. Blinding Effect
6. Pigment on Fibre Surface
7. Batch to Batch Shade Variation
8. Patchy Dyeing Effect
9. Roll to Roll Variation or Meter to Meter Variation
10. Crease Mark
11. Dye Spot
12. Wrinkle Mark
13. Softener Mark
1. Uneven Shade:
Causes:
The reasons for uneven shade are-
• Faulty liquor movement
• Faulty fabric movement during naphtholation
• Improper naphtholation
• Improper hydroextraction
• Uneven pretreatment (uneven scouring & bleaching).
• Improper color dosing.
• Using dyes of high fixation property.
• Uneven heat-setting in case of synthetic fibers.
• Lack of control on dyeing m/c

4. Corrective Action:
By taking this steps we can reduce uneven shade/uneven dyeing-
• By ensuring even pretreatment.
• By ensuring even heat-setting in case of synthetic fibers.
• Proper dosing of dyes and chemicals.
• Proper controlling of dyeing m/c
2. Naphthol Migration:
The naphthol in fabric goes to base solution of the bath and reacts with base there other than in the
fabric. This is called naphthol migration.
Causes:
The reasons of naphthol migration are-
• Improper selection of naphthol
• More moisture in fabric
Corrective Action:
By maintaining these step we can prevent naphthol migration-
• The alkalinity of the naphthol bath shall not drop below the prescribed limit , otherwise the
naphthol may presipitate.
• Formaldehyde shall not be used when working at more than 50 Deg C or when the material is
to be dried after naphthol application.
• Material shall be protected from water spotting,steam,acid and chlorine fumes , and exposure
to sunlight after naphthol application.
• Use of excess salt in naphthol bath may result into precipitation of the bath.
• The temperature is very important in base preparation stem , otherwise diazotization may not
take place.
• Sodium acetate must be added to the developing bath just before the use , otherwise base will
become unstable due to fall in concentration of HCl.
• Hydroextraction time must not be too long , which may result into light spots after
development.
• Material shall be rinsed without delay after developing , otherwise the mechanically held
excess developing liquor will undergo some decomposition and cause deposition of dark
colored spots , which will be difficult to remove.
• It is important to use sufficient amount of alkali binding agents , otherwise it will result into
presipitation of developing bath.
3. Slow Coupling Reaction:
Causes:
The reasons for slow coupling reaction are-
• Improper selection of base to mix with naphthol
• Wrong range of pH in bath, i.e. more acidity.
Corrective Action:
By keeping in mind this step we can reduce slow coupling reaction-
• Use good graded naphthol

5. • Use right range of pH in bath
• Careful about reaction time
4. Afinity of Base Towards Cellulose:
Azoic base should have affinity towards naphthol. But sometime it shows affinity towards cellulose.
This hampers deing.
5. Blinding Effect:
Causes:
In case of azoic dyeing a blinding effect may occur, due to-
• Presence of alkali during naphtholation
• Improper value of pH
• Presence of alkali in coupling bath.
Corrective Action:
• Using prescribed amount of alkali during naphtholation
• Using proper value of pH
• Using proper amount of alkali in coupling bath
• Bath should be clean before dyeing
6. Pigment on Fibre Surface:
Cause:
The reasons for this problem are-
• Unfixed dye on fibre surface
• Improper washing after dyeing
Corrective Action:
By taking this steps we can reduce this problem. They are bellow-
• Using binding agent for alkali
• Curing process.
7. Batch to Batch Shade Variation:
Causes:
The reasons for this problem are-
• Fluctuation of Temperature.
• Improper dosing time of dyes & chemicals.
• Batch to batch weight variation of dyes and chemicals.
• Dyes lot variation.
• Improper reel speed, pump speed, liquor ratio.
• Improper pretreatment.
Corrective Action:
• Use standard dyes and chemicals.
• Maintain the same liquor ratio.
• Follow the standard pretreatment procedure.

6. • Maintain the same dyeing cycle.
• Identical dyeing procedure should be followed for the same depth of the Shade.
• Make sure that the operators add the right bulk chemicals at the same time and temperature in
the process.
• The pH, hardness and sodium carbonate content of supply water should check daily.
8. Patchy Dyeing Effect:
Causes:
Reasons for patchy dyeing effect are-
• Entanglement of fabric.
• Faulty injection of alkali.
• Improper addition of color.
• Due to hardness of water.
• Due to improper salt addition.
• Dye migration during intermediate dyeing.
• Uneven heat in the machine, etc.
Corrective Action:
• By ensuring proper pretreatment.
• Proper dosing of dyes and chemicals.
• Heat should be same throughout the dye liquor.
• Proper salt addition.
9. Roll to Roll Variation or Meter to Meter Variation:
Causes:
Reasons for this problem are bellow-
• Poor migration property of dyes.
• Improper dyes solubility.
• Hardness of water.
• Faulty m/c speed, etc
Corrective Action:
• Use standard dyes and chemicals.
• Proper m/c speed.
• Use of soft water.
10. Crease Mark:
Causes:
The reasons for crease mark are-
• Poor opening of the fabric rope
• Shock cooling of synthetic material
• If pump pressure & reel speed is not equal
• Due to high speed m/c running

7. Corrective Action:
• Maintaining proper reel sped & pump speed.
• Lower rate rising and cooling the temperature
• Reducing the m/c load
• Higher liquor ratio
11. Dye Spot:
Causes:
Reasons for this problem are bellow-
• Improper Dissolving of dye particle in bath.
• Improper Dissolving of caustic soda particle in bath.
Corrective Action:
• By proper dissolving of dyes & chemicals
• By passing the dissolved dyestuff through a fine stainless steel mesh strainer, so that the large
un-dissolved particles are removed.
12. Wrinkle Mark:
Causes:
• Poor opening of the fabric rope
• Shock cooling of synthetic material
• High temperature entanglement of the fabric
Corrective Action:
• Maintaining proper reel sped & pump speed.
• Lower rate rising and cooling the temperature
• Higher liquor ratio
13. Softener Mark:
Causes:
Reasons of happening this effect are down bellow-
• Improper mixing of the Softener.
• Improper running time of the fabric during application of softener.
• Entanglement of the fabric during application of softener
Corrective Action:
By taking these steps we can prevent softener mark-
• Maintaining proper reel sped & pump speed.
• Proper Mixing of the softener before addition.
• Prevent the entanglement of the fabric during application of softener

8. Conclusion:
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. Azoic dyes are used for producing
bright shade of color such as orange, red, scarlet, navy blue, and black color.
---The End---
Submitted by
Md Rakibul Hassan
Id: 183014057
Reference:
http://textileengg.blogspot.com/2015/11/problem-
in-dyeing-with-azoic-color.html
https://textilelearner.blogspot.com/2012/01/dyeing
-of-cotton-fabric-with-azoic-dyes_24.html