Continuous Dyeing of Cotton and Polyester Blend Fabric with Suitable Dyes

Mazharul Islam
Sr. Executive (Solid Dyeing)
M.Sc. in Textile Engineering (DIU – on going)
B.Sc. in Textile Engineering (PTEC-10th Batch ~ BUTex)
Facebook Link: https://www.facebook.com/mazharul.bds

Introduction:
Dyeing is the application of dyes or pigments on textile materials such as fibers, yarns, and fabrics with the goal of achieving color with desired color fastness. Dyeing is normally done in a special solution containing dyes and particular chemical material. Dye molecules are fixed to the fiber by absorption, diffusion, or bonding with temperature and time being key controlling factors. The bond between dye molecule and fiber may be strong or weak, depending on the dye used.

Dyes used for continuous dyeing of cellulosic are as follows-

1. Reactive dyes – 45%
2. Vat dyes – 25 %
3. Sulfur dyes – 15%
4. Others – 15%

Dyes used for continuous dyeing of polyester fabric-

Disperse Dyes:
Blends are any textile material, from fibres or filaments, through yarns to fabric which are deliberate combination of chemically or physically different fibrous polymer. In recent year about hundred possible blends can be obtained from different major textile fibers namely- Cotton, Polyester, Linen, Wool, Viscose, Acetate, Nylon and Acrylic. Some popular blends are-

• CVC/PC/TC or Polyester/cotton: About 60 %
• Polyester/viscose: About 20 %
• Polyester/wool: 8-10 %
• Nylon/wool: 0.8 %
• Acrylic/wool: 7.2 %

In case of CVC or PC/TC dyeing mostly Reactive dyes is used for cotton part and Disperse dyes is used for polyester part dyeing.

And In case of cotton and polyester blended dyeing the one bath is used only for light shade and the two bath process is more suitable to achieve optimum shade (light to Dark). In this case the blend fabric is to achieve different effect on fabric such as solid effect, reverse or resist, cross effect, Ton in Tone & contrast effect.

List of Dyes and Chemicals for Cotton & Polyester Blend Dyeing:

Mechanism of Dyeing with Reactive Dye:
The dyeing mechanism of cotton fabric with reactive dye takes place in 3 stages:

1. Exhaustion of dye in presence of electrolyte i.e. dyes adsorption.
2. Fixation (under the influence of alkali.)
3. Wash-off (remove the unfixed dye from material surface.)

1. Dye exhaustion: When fiber is immersed in dye liquor, an electrolyte is added to assist the exhaustion of dye. Here NaCl is used as the electrolyte. This electrolyte increases the adsorption of dyes. So when the textile material is immersed into the dye liquor, the dye is exhausted on to the fiber.

2. Fixation: Fixation of dye means the reaction of reactive group of dye with terminal –OH or -NH₂– group of fiber and thus forming strong covalent bond with the fiber. This is an important phase, which is controlled by maintaining proper pH by adding alkali. The alkali used for this creates proper pH in dye bath and work as the dye-fixing agent. The reaction takes place in this stage is shown below:

3. Wash-off: As the dyeing is completed, a good wash must be applied to the material to remove extra and unfixed dyes from material surface. This is necessary for level dyeing and good fastness properties. It is done by a series of hot wash, cold wash and soap solution wash.

Mechanism of Dyeing with Disperse Dye:
The dyeing of hydrophobic fibres like polyester fibres with disperse dyes may be considered as a process of dye transfer from liquid solvent (water) to a solid organic solvent (fibre) and the dyeing takes place in the following stages:

1. Dispersion: Dispersion (diffusion) of the dye particles into water by breaking up into individual molecule in the presence of dispersing agents and raise in the temperature.

2. Adsorption: Adsorption of the dissolved dye from the solution on to the fibre surface. The fibre is swollen by using heat energy (raising the temperature above 130ºC+) or Carriers, Temperature depends on the process of dyeing.

3. Diffusion: Diffusion of the adsorbed dye from the fibre surface into the interior of the fibre towards its center. Then the fibre is brought back to its initial compact structure.

Continuous Dyeing:
Continuous dyeing is such a types of dyeing in which the fabric is treated continuously. Continuous dyeing were started which includes enhanced productivity (as high processing speeds of 40 – 80 m/min are possible), better process control leads to better reproducibility, and production flexibility because the lot size could be from 200 m to 20,000 meters and more. This processes is suitable for lightweight to heavyweight fabrics. Besides these followings are the advantages of continuous dyeing.

1. Cost-efficient process.
2. High processing speeds.
3. Lot size could be large compare with exhaust process.
4. Uniformity of dyeing.
5. Enhanced fabric brilliance and luster.
6. Improved levelness and solidity of shade.
7. Good appearance and high color yield.

A Continuous dyeing process typically consists the following:

• Dye application,
• Dye fixation with heat or chemicals and finally-
• Washing.

Continuous dyeing has been found to be most suitable for woven fabrics.

Continuous cotton and polyester Blend Dyeing Process caries:

1. One Bath Process.
2. Two Bath Process.

In case of CVC or PC blended dyeing the one bath process is used only for light shade and the two bath process is more suitable to achieve optimum shade (light to Dark). Continuous cotton and polyester Blend Dyeing caries the PDPS process of dyeing.

One Bath Cotton & Polyester Blend Dyeing Process:

Recipe of Dyes Solution:

• Reactive Dyes = x g/l (Light Shade Only)
• Disperse Dyes = y g/l (Light Shade Only)
• Dispersing Agent = 2-3 g/l
• Leveling agent = 2-3 g/l
• Sequestering agent = 1-2 g/l
• Wetting Agent = 2-3 g/l
• Anti-migrating Agent = 10-15 g/l
• Acetic Acid = 0.5-1 g/l

Flowchart for One Bath Continues Process:

Padding with Suitable Recipe

↓

Infra-Red drying

↓

Thermofix

↓

Cooling

↓

Pad Steam Chemical Padding

↓

Steamer

↓

Washing off & Neutralization

↓

Drying

• Machine Speed 40-60 m/min, Machine Parameter such as Padder Pressure, Chamber Temperature and Blower – depend on the construction of the Fabric.
• Padding with disperse and reactive dye at 20-30°C. Liquor pick up 60-80%.
• The temperature in Infra-Red drying is around 650-700°C, time around 20 sec, residual moisture 30%, it is done to avoid migration of dyes.
• Thermo-fixation: It is done at 120-180°C, 30-45sec. It is the fixation step of polyester part. The Temperature of last chamber is 170-180°C.
• Dye fixation takes place during steaming. The Development Padding (at Pad Steam) is done by using-
  • Glauber Salt – 250 g/l
  • Caustic Soda – 1-3 g/l
  • Soda Ash–20 g/l.
• The temperature in the steaming is 101°C -103°C and time is 60s-120s. The goods are then washed-off & Neutralization and then drying.
• Wash-off Bath:
  • (Bath 01) Normal Temperature (30°C) Wash.
  • (Bath 02) Medium Hot Wash (70°C).
  • (Bath 03) Hot Wash (90°C). with Soaping Chemical
  • (Bath 04) Hot Wash (90°C). with Soaping Chemical
  • (Bath 05) Hot Wash (90°C) with Soaping Chemical 3-5 g/l
  • (Bath 06) Hot Wash (90°C).
  • (Bath 07) Medium Hot Wash (70°C).
  • (Last Bath-08) Normal Temperature (30°C) Wash with Acetic Acid 0.5-1 g/l
• By this process blended dyeing is complete.

Two Bath Cotton & Polyester Blend Dyeing Process:
Two steps for continues blend dyeing process are given below:

1. Step 1 for Polyester Part dyeing with Disperse Dyes.
2. Step 2 for Cotton Part dyeing with Reactive Dyes.

Step 1 for polyester part:

Recipe of Dyes Solution for Polyester Part-

• Disperse Dyes = x g/l
• Dispersing Agent = 2-3 g/l
• Leveling agent = 2-3 g/l
• Sequestering agent = 1-2 g/l
• Wetting Agent = 2-3 g/l
• Anti-migrating Agent = 10-15 g/l
• Acetic Acid = 0.5-1 g/l

Flowchart for Polyester Part Continues Dyeing:

Padding with Disperse dyes with Auxiliaries

↓

Infra-Red drying

↓

Thermofix

↓

Cooling

↓

Pad Steam (R/C) Chemical Padding

↓

Steamer

↓

Washing off & Neutralization

↓

Drying

• Machine Speed 40-60 m/min, Machine Parameter such as Padder Pressure, Chamber Temperature and Blower – depend on the construction of the Fabric.
• Padding with disperse dye at 20-30°C. Liquor pick up 60-80%.
• The temperature in Infra-Red drying is around 650-700°C, time around 20 sec, residual moisture 30%. it is done to avoid migration of dyes.
• Thermo-fixation: It is done at 160-250°C, 30-45 sec. It is the fixation step of polyester part. The Temperature of last chamber is 220-280°C.
• At Pad steam Machine, Reduction Cleaning (R/C) is done by the Chemical, combination of Sodium Hydro Sulphite (Hydrose) = 40-60 g/l and Caustic Soda (NaOH) = 40-60 g/l.
• The temperature in the steaming is 101°C -103°C and time is 60s-120s. The goods are then washed-off and dry. Machine Speed 50-60 m/min. Here the unfixed dyes on cotton part is removed by R/C and Wash off (with 8 chamber of wash bath which is given above).
• Here neutralization is done by Acetic Acid (0.5-1g/l) at the Last wash chamber.
• By this process polyester part dyeing is complete.

Step 2 for cotton part:

Recipe of Dyes Solution for Cotton Part-

• Reactive Dyes = x g/l
• Leveling agent = 2-3 g/l
• Sequestering agent = 1-2 g/l
• Wetting Agent = 2-3 g/l
• Anti-migrating Agent = 10-15 g/l

Flowchart for Cotton Part Continues Dyeing:

Padding with Reactive dyes with Auxiliaries

↓

Infra-Red drying

↓

Thermofix

↓

Cooling

↓

Pad Steam Development

↓

Washing off

↓

Drying

• Machine Speed 40-60 m/min, Machine Parameter such as Padder Pressure, Chamber Temperature and Blower – depend on the construction of the Fabric.
• Padding with reactive dye at 20-30°C. Liquor pick up 60-80%.
• The temperature in Infra-Red drying is around 650-700°C, time around 20 sec, residual moisture 30%. it is done to avoid migration of dyes.
• Thermo-fixation: It is done at 80-140°C, 30-45 sec. The Temperature of last chamber is 120-150°C.
• Dye fixation takes place during steaming. At Pad steam Machine, The Development Padding is done by using
  • Glauber Salt – 250 g/l
  • Caustic Soda – 3-10 g/l
  • Soda Ash–20 g/l.
• The temperature in the steaming is 101°C – 103°C and time is 60s-120s, Machine Speed 50-60 m/min. The goods are then washed-off and dry. (Washed with 8 chamber of wash bath which is given above).
• By this process blended dyeing is complete.

References:

1. https://textilelearner.net/continuous-dyeing-process-thermosol-and-pad-steam/

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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.

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