Continuous Dyeing Process: Thermosol and Pad Steam

Mazharul Islam
Sr. Executive (Solid Dyeing)
M.Sc. in Textile Engineering (1st Semester)
B.Sc. in Textile Engineering (PTEC – 10th Batch)
Email: [email protected]

What is Dyeing?
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.

Methods of Dyeing:
There are mainly three methods of dyeing:

1. Exhaust Dyeing
2. Semi-Continuous Dyeing
3. Continuous Dyeing

Continuous Dyeing Machine:
Continuous dyeing machine is such a types of dyeing machine in which the fabric is treated continuously.

**A Continuous dyeing process typically consists the following:

1. Dye application,
2. Dye fixation with heat or chemicals and finally
3. Washing.

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

Name of machine which is used for continuous process:

1. Pad Thermosol machine.
2. Pad Steam machine.

Thermosol Dyeing:
Thermosol machine is used to dye fabric from Light to Dark shades. It is based on method to dry to dry the fabric without any contact with steaming. This machine is able to carry the following processes:

1. Reactive dyeing
2. Disperse dyeing
3. Vat dyeing
4. Pigment dyeing

Here reactive dyeing is followed two processes:

1. PDPS (Pad Dry Pad Steam).
2. PDC (Pad Dry Cure).

Disperse Dyeing Process caries:

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

Suitable Woven Fabric for Thermosol Dyeing:

• 100% Cotton.
• Cotton + Spandex.
• Polyester.
• CVC.
• PC/TC.
• Linen.
• Linen Cotton Blend.

Machine Specifications:

• Manufacture: Monfongs Thermex/ Monforts Monotex
• Production Speed: 40-60 m/min
• Padder: Kuster Dye Pad
• Chambers: 3 or 5 (depend on Manufacturer)
• Trough Capacity: 25-30 liters
• Padder Pressure (N/mm): 20-30-20
• VTG/Airing Zone: 20m of fabric
• IR Temperature: Range 650°C-850°C
• Liquor Change: After 3-4min

Follow Chart of Thermosol Process:

Batcher/Plate (fabric feed)

↓

J-Box

↓

Cooling Drums

↓

Padding

↓

Airing (Penetration/migration)

↓

IR (Pre-Drying)

↓

Drying & Curing (Thermo-fixation)

↓

Cooling Drums

↓

J-Box

↓

Batcher/Plate (fabric out)

1. J-box:

• It stores the fabric.
• It is J-shaped metal holder for fabric.

2. Guide roller and Guider:

• These rollers are steel rollers used to guide the fabric and to provide tension which prevents the crease formation.
• Guider is rubber coated roller is placed at edge of fabric to prevent and control the width of fabric.

3. Compensator:
These are used to provide tension to the fabric. If the fabric loosens from any roller during the process, this moves up and down to maintain the tension.

4. Dye Padder:

• The padder is mechanical mean of applying dye on fabric.
• The padding operation consist of two parts:
  • First immersion of the fabric in dye-liquor in a trough and
  • Second passing the fabric between the two padder to force the dye-liquor into the fabric and also to squeeze excess amount liquor back to the trough.
• Padder is the most sensitive components dyeing system as any fault developed at the padding stage will not be corrected later.

5. Nip rolls:

• Nip rolls must be clean.
• The hardness for woven is 70-80 degree shore and 50-60 shore for knitted fabric.
• The padder roll has a steel mandrel that is covered with hard rubber.
• Both the rollers should have exactly the same hardness otherwise there will be color difference in the face and back side of the fabric.

6. Pick up and speed:
The pickup% for the different fabric are

• Cotton = 55-70%
• P/C (50:50) = 45-50%
• Viscose = 85-95%
• Linen =  55-70%

7. Padding Trough:

• The trough is placed below and in front of the padder.
• It is U-shaped box with one or more free-running guide rollers of about 10cm diameter each.
• The volume in the pad trough should be relatively small 20-50 liters
• Resulting in shade difference caused by variations in immersion time and pick up.
• The pad liquor turnover time should be as fast as possible less than 5minutes.
• Immersion time: Should be 1-2s

8. Airing zone:

• Airing zone is used because sometimes the light GSM fabric has face and back variation so we used airing zone.
• The airing zone is placed between the padding and drying for better swelling and penetration of the dye
• These rollers are Teflon coated to avoid stains on the fabric due to rusting and stickiness of chemical.

9. Infra-Red Pre-Dryer:

• The intermediate drying phase. Temperature Range 650°C-850°C.
• To get even and uniform results especially for medium and deep shades.
• Dye molecule tend to diffuse with water molecule as they migrate from the wetter towards the drier part if the fabric.
• Migration stops when only bonded water molecules and moisture content of the fabric dropped below 30%

10. Requirement of an Infrared pre-driers:

• Gas or electrically heated.
• The emitted IR wavelength should correspond maximum absorption value of water (3µm).
• Equilibrium setting uptime.
• Air passage before pre-drying (dye penetration).
• Cleaning of guide rollers

11. Thermo fixation:
In the thermo fixation (also incorrectly called thermosol) process of dyeing, The cotton fabric dyeing temperature range 100°C-160°C which is depend on the process of dyeing. For synthetic fabric the disperse dyes diffuse into the polyester fibers on bringing the dye-padded fabrics to temperature of 200-280°C for a contact time of 60-30 seconds because the polyester has the compact structure and having 85% of crystalline area so at high temperature the pores of the fiber are open which allows to enter the dye in the highly crystalline area.

12. Drying chambers:

• There are three or five drying chambers (depend on manufacturer).
• There is water blower which sucks air from the atmosphere and circulates that air by centrifugal action in whole chamber.
• There is a gauge on each dryer which is showing the balance of air inside the chamber.

13. Curing Chambers:

• There are total two curing chamber i.e. used when dyeing with polyester or with disperse otherwise as a drying chamber.

14. Cooling drum:

• These are provided at the inlet and outlet side of the thermosol machine.
• These are hollow steel drums and used to maintain the temperature of the whole lot water filled inside the drum to cool it.

A Short Description of Continuous Dyeing Process:

1. PDC (Pad – Dry – Cure) Process:

• This is a Salt – free and continuous one–bath method.
• Applicable only for pale to light series shades.
• In this process, reactive dye is padded on to cellulose in the presence of Soda Ash (Na₂CO₃) – 20-30 g/l and Urea (40 – 50 g/l).
• After drying dye fixation is carried out in a curing chamber at 130°C – 160°C for 2-5 min depending on the depth of the shade.
• Then washing–off is carried out at Continuous wash machine.

2. PDPS (Pad Dry – Pad Steam) process:

• It is a double pad process. Classic procedure for dyeing of Light to Extra Dark Shades of woven fabrics. Main advantage of the pad–dry–pad–steam process are:
  • High productivity
  • Good appearance
  • High color yield
• Process: Padding with dyes & Auxiliaries – Infra-Red drying – Thermofix – Pad Dry Fabric – Pad Steam – Washing off – Drying.
• Pad liquor temperature is 20°C – 30°C. Modified padding mangles are used in both cold brand and hot brand reactive dyes can be used in this process.
• Liquor pick up 50 – 80%
• Drying at 100°C -150°C in hot flues depend on Shade and GSM of fabric.
• Chemical Pad (Salt 200-250 g/l with Caustic Soda 3-10g/l and Soda Ash 20g/l) on a padder.
• Pad liquor temperature is 20°C – 25°C
• Liquor pick up 60 – 80%
• Steaming 60 – 120 sec in saturated steam. It is done in a dyehouse steamer. Dye fixation takes place during steaming Temperature 101°C-103°C. The goods are then washed-off and dry.

3. PDPS of Disperse And Reactive Dyes:
It is the process for continuous dyeing of Polyester-Cotton blends. It may be either disperse reactive combination or disperse vat combination.

• One Bath Process.
• Two Bath Process.

Following is the flow chart:

• For One Bath Process:
  Padding with disperse & reactive dyes with Chemical & Auxiliaries – Infra-Red drying – Thermofix – Pad Steam -Washing –off – Drying.
• For Two Bath Process:
  • Step 1 for Polyester Part: Padding with disperse dyes with Auxiliaries – Infra-Red drying – Thermofix – R/C (Pad Steam) – Washing off – Drying.
  • Step 2 for Cotton Part: Padding with Reactive dyes with Auxiliaries – Infra-Red drying – Thermofix – Pad Steam – Washing off – Drying.
• The temperature in infra-red drying is 650°C, time 45-60 sec, residual moisture 30%
• The temperature in thermosol is 180°C -280°C and time is 15-30 sec.
• 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 Second Padding is done by using Gluber 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. The goods are then washed-off and dry.

4. PDPS of VAT Process:
I have also published an article on Continuous Vat Dyeing Process. You can read this.

Pad Steam Process Follow Chart

Batcher/Plate (fabric feed)

↓

J-Box

↓

Dansing

↓

Padding

↓

Steamer Mouth

↓

Steamer (101°C -103°C)

↓

Water lock

↓

Master Padder

↓

Washing Bath

↓

Master Padder of Wash

↓

Dryer

↓

Fabric out

References:

1. Wikipedia.
2. Textile Journal-Different Dyeing Process.
3. https://www.academia.edu.
4. Chemistry of Dyeing / D.P. Chattopadhyay, in Handbook of Textile and Industrial Dyeing, 2011.

You may also like:

1. Sustainable Dyeing Process in Textile Industry
2. Cold Pad Batch (CPB): A Sustainable Dyeing Process for Woven and Knit Industry

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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