Carrier method of dyeing for polyester fabric is done at atmospheric temperature with disperse dye. Disperse dyes are non-ionic in nature, almost insoluble and stay as finely divided aqueous dispersed form in water.
These dyes have inherent affinity for polyester. In case of disperse dye, the pH and temperature should be carefully controlled. But cationic dye able polyester can be dyed with basic dye also. It can be hydrolyzed in high temperature especially under alkaline conditions.
But dyeing with disperse dye is carried out in acidic medium in the presence of dispersing agent. Dye diffusion can be obtained either using a suitable carrier or providing high temperature and pressure.
Dye carriers enable polyester dyeing at atmospheric temperature. Carriers help to increase dye up take and level dyeing at atmospheric temperature below 100℃.
Though they helps in level dyeing, some unwanted features of carrier cease out or lessen the practical use of this process nowadays.
In carrier method of dyeing, carrier swells the polyester fiber and create free volume inside the fiber polymer. They assist in transfer of the dye molecules from dye solution into the fiber.
After the migration of dyes into the fiber, the bath temperature needs to reduce slowly, then the swelled fiber becomes solid and the migrated dye molecules are mechanically trapped into the fiber structure.
Factors influencing level dyeing
- pH of dye solution
Commercially, polyester dyeing with disperse dye is carried out at pH 5-6. Some industries strictly follow 4.5 pH. But strong alkaline or acidic pH like more than 9 or less than 4 is not feasible at all. Because at strong alkaline pH, polyester fiber undergoes degradation and losses a part of it. Again, alkalinity decreases the percentage exhaustion of some azo disperse dyes. The hydrolysis of polyester and azo disperse dye is accelerated at high temperature.
- Dye particle size
The size of dye particles in the dispersion medium plays an important role in dye adsorption. With a reduction in dye particle size helps to increase the dye solubility and adsorption.
- Absorption of carriers
Hydrophobic carriers are more effective on polyester. The carriers having ionizable or solubilizing group are less effective. Carriers can easily absorbed by non-polar force between the aromatic region of fiber and carrier.
The absorption and dye diffusion depends on the temperature greatly. In case of synthetic fiber dyeing, glass transition temperature is an important factor. It is responsible for the movement of polymer chain. Below 100℃, polyester dyeing process take longer time.
Dyeing Recipe of Carrier Method of Dyeing
|Carrier (Phenol)||2 – 5%|
|Dispersing agent||0.5 – 1.0 g/L|
|Levelling agent||1.0 – 2.0 g/L|
|Sequestering agent||1.0 – 2.0 g/L|
|Acetic acid ( 50% )||0.5 – 2 g/L|
|pH||4 – 5.5|
|Temperature||90 – 100℃|
Process description of carrier method
- Preparation of dye solution
As disperse dyes are water insoluble, you can’t dye your stuff with it until you make it dispersible (partially soluble) solution by a rapid stirring with water (around 45℃) that would be warm enough. Add some dispersing agent and stir promptly until you get the uniform mixture of dyes.
- At 50℃ the bath can be set up with substrate and then add the accounted amount of dispersing agent, carrier, acetic acid and other auxiliaries, then keep the dye bath last for 5-10 min.
- Add dye solution gradually and elevate the temperature up to 90-100℃ at 1-2℃/min.
- At the same temperature keep the bath running for at least an hour.
- Slowly decrease the bath temperature to 70-80℃ over 10-15 min.
- Drop the dye bath followed by the after-treatment process.
- After-treatment Process
- Firstly, rinse with hot water then followed by cold water.
- For deep shade carry out the following treatment with-
Caustic soda (36˚Be) – 2-6 ml/L
Sodium Hydrosulphit (Hydroze)- 1-3 g/L
At 70℃ for 10-15 min. The used amount of caustic soda and hydroze may be higher depending on the shades. The after-treatment process that is carried out with caustic and hydroze to remove unfixed disperse dyes from the substrate is called “Reduction Cleaning”.
- Again rinse with hot water and end up the procedure with cold water rinsing.
- With acetic acid, the substrate must be neutralized.
Dyeing process curve
Image Source: Practice of Textile Coloration
Fig: Dyeing of Polyester fabric with disperse dye using carrier method
Advantages of Carrier method
- Dyeing can be done at atmospheric temperature and normal pressure.
- Lower dyeing time can be achieved.
- As Polyester is highly crystalline fabric, it was difficult to produce deep shade on polyester earlier. But with carrier medium to dark shades can be produced easily.
- Carriers can improve dye uptake on materials.
- In case of polyester-wool blend, some carriers help in reducing staining of wool.
Drawbacks of Carrier method
- Carriers are toxic and un-hygenic in nature that can cause skin irritation.
- Use of carrier in dyeing adds to an extra cost.
- As, the cost of carrier and for removal of carrier, alkali is required. Thus it increases in cost.
- Carriers alters the light fastness of dyed materials.
- It causes shrinkage of materials.
- Some carrier have bad odor.
- Condensation of carrier vapor and brake down of carrier emulsion can cause possible source of faults such as oily spots.
- Some carriers are dye specific and can exhibit different efficiency with different dyes.
To Wrap Up!
Atmospheric dyeing of polyester with disperse dye is possible only with the dyeing carriers. It also helps in producing deep shades on polyesters. Though carrier method has some drawbacks, it helps in dyeing of hydrophobic fibers at lower temperature.
HTHP method is extensively used in our textile industries. Though the three dyeing methods- carrier method of dyeing, HTHP method or Pad- thermosol method are used for polyester dyeing, there are some basic differences among them which makes the HTHP method more suitable for polyester.