Disperse Dyeing Process: Properties & Mechanism

What is Disperse Dye?

Disperse dye is an organic coloring substance that is free from ionizing groups, with low water solubility & suitable for dyeing hydrophobic textiles. It is used for dyeing man-made fibers. The dye is so called because it is non-soluble, non-ionic dye & molecularly dispersed.

Properties of Disperse Dyes:  

✔ Disperse dyes are molecularly dispersed.  

✔ Less soluble in water which makes fine dispersion.  

✔ The light fastness of dispersed dye is fair to good (rating 4-5).  

✔ Washing fasters is moderate to good (rating 3-4). 

✔ Good sublimation power due to its stable electron arrangement. 

✔ No sulphonate group.  

✔ Color will fade due to heat application on disperse dye.  

Types of Disperse Dyes:  

• Based on the form: Two forms of these dyes 

1. Pure dyes 
2. Readymade dyes (with dispersing agent) 
3. Solid dyes 
4. Liquid dyes 

• Chemical Classification: 

1. Azo dyes: 
2. Mono azo dyes: 

NO2 N N NH2 

e.i. Disperse orange 

1. Diazo dyes: 

N N N N OH 

Sulpracel Golden Orange GR 

1. Triazo dyes 
2. Anthraquinone dyes: 
   

NH2 NH2 

O O 

NH2 NH2 

C.I. Disperse blue 

3. Other dye: 
4. Aminoketone dyes: 

O NH 

O N O CH2 

Celliton Fast Green 3B 

1. Nitro dyes: 

NO2 

NO2 NH 

Serisol Yellow-2G

Commercial Name of Dispersed Dyes:  

Name Manufacturer Country 

1. Terasil Cibageigy Switzerland 
2. Foron Sandoz Switzerland 
3. Palanil BASF Germany 
4. Resonil Bayer Germany 
5. Dispersal ICI UK 

Mechanism/Chemistry of Disperse Dyeing:  

▪ Dyeing of hydrophobic fibers like polyester fibers with dispersed dyes may be considered a process of dye transfer from a liquid solvent (water) to a solid organic solvent (fiber).

▪ Disperse dye is added to water with the surface active agent to form an aqueous dispersion. ▪ The insolubility of dispersed dyes enables them to leave the dye liquor as they are more substantive to the organic fiber than to the inorganic dye liquor.  

▪ Heating of dye liquor swells the fiber to some extent and assists the dye to penetrate the fiber polymer system. Thus the dye molecule takes its place in the amorphous parts of the fiber. Once taking place between the fiber polymer system, the dye molecules are held by hydrogen bonds and Van Der Waals’ force. 

Methods of Application of Disperse Dyes: 

1. Method N: Normal temperature dyeing (80-100°C) 
2. Method NC/Carrier method: Normal temp dyeing with carriers (80 – 100°C). 
3. Method HT: High temp dyeing (105° – 140°C)  
4. Method T: Thermosol method (180° – 200°C)  
5. Pad-batch method: Semi-continuous method.  
6. Pad-steam method: Continuous method.  

Dyeing of Polyester Fabric With Dispersed Dye by Carrier Method: 

▪ Recipe:  

Dye: x% owf  

Carrier: 1-4% owf  

Dispersing agent: 0.5-1% 

Wetting agent: 1-2 g/l  

Acetic acid: 1-2g/L (PH: 4.5- 5.5) 

M:L = 1:10 

Temp: 100°C, Time: 1 hr.  

▪ Dye solution is prepared with cold water  

(1:10) & kept for 15 mins.  

▪ Dye bath is set at 60°C & carrier, dispersing agent & salts are mixed one by one.  ▪ Material is added & kept for 15 mins without raising the temp.  

▪ The dye solution is added and pH is controlled with CH3COOH. 

▪ The temp is raised up to 100°C. Then dyeing is continued for the required time of 1 hr.  ▪ The temp is lowered to 70°C, then rinsed and reduction clearing if required.  

Advantages of the Carrier Method:  

✔ Possibility of dyeing in simple dyeing equipment at atmospheric pressure at temp of up to 100° C for polyester fiber.  

✔ Reduced dyeing cycle due to accelerated dyeing.  

✔ Improved fatness properties due to increased perpetration in the fiber. 

✔ Moderate level dyeing in polyester dyeing.  

✔ Increased rate of dyeing & increased leveling.  

✔ Some carriers reduce the staining of wool while dyeing polyester/wool blends. 

Disadvantage of Carrier Method:  

✔ More costly. 

✔ Removing of carrier by using alkali also causes more cost.  

✔ Decreased light fastness.  

✔ Toxicity of some carriers. 

✔ Odor and air pollution problem. 

✔ Some can cause carrier spots.  

Dyeing of polyester with dispersed dye by HT Method (Most common Method): 

• Recipe:  

Dye: x% owf  

Dispersing agent: 0.5-1% 

Salt: 0.5-1% 

Acetic acid: 0.75-1 g/L (PH: 4.5-5.5) 

M:L = 1:8 

Temp: 130°C, Time: 1 hr.  

• The dye bath is set at 60°C & dispersing agent  

▪ Salt is added, fabric is treated for 15 minutes.  

▪ The dye solution is added & PH is controlled with CH3COOH. 

▪ Temp. of the dye bath is raised up to 130°C for 30 mins. & treated at 130°C for 1 hr.  ▪ Then dye bath is cooled as early as possible.  

▪ The fabric is allowed hot rinsing & reduction cleared if required as before.  

Advantages of the HT Method:  

✔ Dyeing times are frequently shorter. 

✔ No need for a carrier. 

✔ Maximum (98%) dye fixation & loss of dye is less. 

✔ Light fastness and wet fastness are usually higher. 

✔ Better exhaustion and deeper dyeing can be produced.  

Disadvantages of the HT Method:  

✔ Higher temp required. 

✔ More control is required. 

Dyeing of Polyester With Dispersed Dye by Thermosol Method: 

▪ Recipe:  

Dye: x% owf 

Thickener: 20-40 g/L 

Wetting agent: 1-2 g/L  

Acetic acid: 1-1.5 g/L (PH: 4.5-5) 

Temp: 180-220°C, Time: 2 hr.  

▪ Process sequence: Padding of fabric → Drying (90°-100°C) → Curing/Thermo fixing (180- 220°C) → Washing. 

▪ The fabric is padded with dye solution & dried at 100°C.  

▪ Fixation is done at 180-220°C for 60-90s depending on fiber type, dye & depth of shade.  ▪ Soap washing or reduction cleared if necessary as before. Finally washed & dried. 

Advantages of the Thermosol Process:  

✔ Dyeing time is very short.  

✔ No need for a carrier. 

✔ Non-toxic. 

✔ Very bright shade is obtained.  

✔ Excellent dye utilization (75-90%) is achieved. 

Disadvantages:  

✔ Shade may be changed due to sublimation at high temp.  

✔ Special machine required.  

✔ Loss of strength when the time of treatment is prolonged.  

✔ Costly due to this process requires special arrangement.  

After Treatment: 

▪ Reduction clearing is done in case of medium & deep shade to improve wash fastness with the following recipe 

Detergent: 1 g/L 

Sodium Hydrosulfite: 2 g/L  

Caustic Soda: 1-2 g/L 

Time: 20-30 min. Temp: 70-80° C  

M:L = 1:30 

▪ Soaping recipe 

Soap/Sando clear PC: 1 g/l 

Temp: 60°C, Time: 30 min 

M:L = 1:30 

Difference Between Carrier, HT & Thermosol Methods:  

Carrier Method	HT Method	Thermosol Method
Neither carrier nor thickener is used.	Carrier is not used, but thickener is used.	Costly as the carrier used.
Dyeing Temp: 80°-100°C	Dyeing Temp: 105°-140°C	Dyeing Temp: 180°-220°C
Costly as carrier used.	Not so costly/Cheap.	Costly as special arrangement required.
Toxic & unhygienic.	Non-toxic & hygienic.	Non-toxic & hygienic.
More shrinkage.	Most shrinkage.	Less shrinkage.
Less production.	Less production.	High production.

Factors Affecting the Dyeing Performance of Disperse Dyes:  

✔ Carrier.  

✔ Dispersing agent. 

✔ Temperature. 

✔ PH. 

✔ Time. 

✔ Type of material to be dyer. 

✔ Quality & chemical groups of dyes.  

Carrier: Carriers are dyeing assistants that alter the dispersing properties of dyes & physical characteristics of the fiber so that more dye can be transferred from the dye bath to the fiber. It is an organic compound that acts as a substantive swelling agent. In the case of hydrophobic fiber such as polyester, a fiber carrier is added to the dye bath or print paste to increase dye take-up.  

Factors Considered For The Selection of Carriers:  

✔ High carrier efficiency. 

✔ Cheap & available at market.  

✔ Non toxicity. 

✔ Little or no effect on the light fastness of the dyeing. 

✔ No degradation or discoloration of the fiber.  

✔ High stability under dyeing conditions.  

✔ Compatibility with the dyestuff.  

✔ Easy dispersion in the dye bath.  

✔ Ease of removal after dyeing.

Function/Mechanism of Carrier:  

• Carriers swell fiber & ultimately cause relaxation. They may act as molecular lubricants. 
• They increase the solubility of the dye.  
• They also make dye film on the surface of the fiber. 
• The carrier transports the dye to the fiber by dye carrier association in the dye bath. 
• Carrier penetrates inside the fiber polymer chain and thereby reduces inter-chain attraction and dye molecules enter the polymer structure. 
• Increase dye take up by covalent bond of fiber liquid.  

Dispersing agent: Dispersing agents help to maintain the dispersion of dye molecules in the dye bath.  The actual dye is farmed as relatively large particles during the last stages of its manufacture  & in this form, it is unsuitable for application on hydrophobic fibers. If these big particles are used without dispersing agents, they may produce uneven dyeing and their full-color value may not be realized.  

Function of Dispersing Agent:  

✔ It assists in the process of particle size reduction of the dye.  

✔ It enables the age to be formed in the powder form.  

✔ When the powder is added to the dye bath, it facilitates the re-conversion of the power into a dispersion that is required for carrying out the dyeing.  

✔ It maintains the dispersion in a fine form in the dye bath throughout the dyeing process.  ✔ It increases the solubility of the dispersed dye in water.  

✔ It affects the rate of dyeing.  

Trade Name of Dispersing Agent: 

Name Manufacturer 

Setamol BASF  

Edalon Sandoz  

Hispogal Hoescht