Application of disperse dyes on 100% Polyester and its blends with cotton and viscose

General process sequence for PC blended fabric is:

 

 

 

Recipe:

• Disperse dyestuff = x %
  
• Nugen LFT = 0.5 %
  
• Acetic Acid = 1.5 %
  
• Carrier = 0.5%
  

If the recipe contains a Navy Blue dyestuff, then pH should 4.5 to 5.0 during dyeing, otherwise navy will tend to exhaust partially and hence unlevel dyeing. (If Formic Acid is available replace Acetic acid 1.5% with 1.0% of it, it is the most stable acid at high temperatures rather than Acetic).

Nugen DFT concentration need not be increase more than 0.5%. It is in fact, leveling and retarding agent; that will impair the depth and fastness.


Dyeing Procedure:

1. Pretreatment:
   
   1. Acetic Acid = 1.5 g/l
      
   2. Nugen DFT = 0.3 g/l
      1. Treat at 50⁰C for 10 minutes
         
2. Dyeing:
   
   1. Add dissolved disperse dye solution at 50⁰C = addition time = 10 minutes
      
   2. Raise the temperature to 115⁰C @ 2⁰C/minute; at 115⁰C hold for 10 minutes
      
   3. Raise the temperature to 135⁰C @0.5⁰C/minute; at 135⁰C hold for 30 to 45 minutes
      
   4. Cool to 80⁰C and drain
      
3. Reduction Clearing:
   
   (Alkaline)
   
   
   1. Caustic Soda = 2 gpl
      
   2. Hydros = 2 gpl
      
   3. Dispersol VLH = 1 gpl
      
      1. Treat at 50⁰C for 20 minutes
         
      2. Cold wash – Acetic acid wash with acetic acid – 1 gpl 10 minutes.
         
   (Acidic)
   
   
   1. Cyclonon ECO = 2gpl
      
   2. Acetic Acid = 2 gpl
      
      1. 
         Treat at 80⁰C for 20 minutes
         
      2. Cold Wash 10 minutes; unload.
         

Please find below a general process sequence for Polyester Cotton blend:

Process Flow for PC and PV blends:

 

 

 











Some reasons for un-level dyeing:

• Highly pH sensitive disperse dyes – almost all navy's and blacks
  
• Too much loading
  
• Liquor Circulation problems
  
• Improper heat setting/no heat setting
  
• Too less quantity of Leveling /dispersing agent
  
• Inadequate quantity of Acetic/Formic acid (please check acid concentration- acetic acid is being manufactured from different sources.) pH plays a major role in disperse dyeing levelness – take care.
  

Other Defects noticed in polyester dyeing:



Moire Effect on PC or PV – woven/knitted:

A watered, clouded, or frosted wavy appearance produced upon either woven or knitted textile fabrics is said to be moiré effect.

The moiré effect is caused mainly due to the differential shrinkage of polyester and cotton or viscose at high temperature and high pressure dyeing. This problem can be avoided by taking proper precautions before and after dyeing.

1. A perfect head setting on pins at a temperature of 200 to 210⁰C for 30 to 45 seconds with an over feed of 6 to 8% may be done.
   
2. In case of PV blends, caustizisation with 10 to 12⁰TW of caustic soda at room temperature may minimize moiré effect.
   
3. Moire effect after dyeing may be corrected either by caustizisation or treating the fabric with 3 to 5 gpl of carrier at 130⁰C for 30 minutes in a jet or soft-flow machine.
   
4. This can also be corrected by subjecting the fabric to high temperature at 200⁰C with an over feed of 6 to 7% and redye in HT + HP machine using 10% of disperse dye recipe for 30 minutes.
   

Poor Sublimation Fastness:

• Some of the disperse dyes tend to crystallize while cooling down the exhausted bath from 135⁰C to 80⁰C. 100⁰C is the most critical temperature at which some of the red disperse dyes ( C.I.No. 53, 60, 131, 132 and 159) give problem of crystallization when they are dyed at higher depths and especially if the dyeing is carried out in hard water. The hardness of water should be nil for disperse dyeing.
  
• Some of the disperse dyes are very sensitive to metal ions and shade changes considerably bluer to duller side. Spinning assistants, spinning oils, alkaline residues and other factors cause crystallization of disperse dyes to produce dye specks. This problem may be solved by proper pretreatment.
  
• The chromophore of the azo based disperse dyes is reduced and become soluble when an alkaline reducing agent (caustic & hydros) at 60C thus promoting poor sublimation and rubbing fastness
  
  Na2SO4 + 2 H2O -------à 2H + 2NaHSO3
  
  (alkaline condition)
  
  -N=N- + 4H --------à -NH2-NH2- (soluble disperse dye)
  
  Azo dye
  
• Use of non-ionic auxiliaries in the dye bath may also tend to aggregate some of the disperse dyes causing poor sublimation and rubbing fastness.
  

These problems can be overcome by using the following recipe:

• Disperse dye = x %
• Acetic acid = 1.0 gpl
• Sodium Acetate = 0.5 gpl
• Anionic dispersing agent = 1.0 gpl
  

Or

• Disperse dye = x %
  
• Formic acid = 0.35 to 0.5 gpl
  
• Ammonium Sulphate = 1.0 gpl
  
• Anionic dispersing agent = 1.0 gpl
  

Dye Specks:
Dyeing auxiliaries like carrier, leveling agents (non-ionic) are liable to nullify the effect and impair the solubilizing effect of dispersing agents thus promoting aggregation and agglomeration of disperse dyes causing specks.
Also use of non-ionic silicones during final finishing tend to aggregate disperse dye and reactive dyes; reduces the sublimation /rubbing fastness of the dyed fabric.
Non-ionic products in the form of wetting, leveling and finishing agents may be curtailed to avoid these problems.


Pilling:
Factors responsible for pilling:

1. Fiber Characteristics such as morphological, chemical and fine structure of the fiber, fiber length, fineness, strength etc.
   
2. Yarn Characteristics – viz., blend, count, twist, hairiness
   
3. Fabric Characteristics – such as weave, ends and picks etc.
   
4. Frictional and abrasive force – such as linear or rotational rubbing forces encountered during wear or processing.
   

Remedies:

• Surface treatment: The protruding fibres from the yarn or fabric can be removed mechanically/chemically or by burning out or cropping, surface carbonizing, singeing, heat setting etc reduces pilling.
  
• Steaming & cropping: the loose projecting fibres are removed mechanically by sharp blades from the surface of the fabric to a certain extent and that helps in reducing pilling.
  
• Surface carbonizing: In this technique, the protruding fibres are burnt or dissolved with suitable chemicals – the nature and the amount of chemicals used depends on the constituents of the blended fabrics. The fabric is thus not only free from pilling but also gives surface feel.