Thermosol Dyeing Process – Advantages, Steps & Key Parameters

The Thermosol dyeing process is one of the most widely used continuous dyeing methods for polyester and polyester-blended fabrics. It is commonly applied for fabric dyeing, printing, and finishing, especially when high production speed and consistent shade are required. Unlike exhaust dyeing, Thermosol uses heat fixation to drive disperse dyes into the polyester fiber, ensuring excellent fastness and uniformity.

This article explains the Thermosol process in detail, including advantages, step-by-step workflow, important parameters, and practical tips for achieving the best results.

 

What is the Thermosol Dyeing Process?

The Thermosol process is a continuous dyeing method where disperse dyes are padded onto polyester fabric and then thermofixed at high temperature (usually 190–210°C). Heat causes the polyester fiber to swell and the dye molecules to diffuse inside, creating a strong bond.

It is mainly used for:

• 100% Polyester fabrics
• Polyester–cotton (PC) blends
• Polyester filament fabrics
• Woven and knitted polyester

 

1. Advantages of the Thermosol Dyeing Process

The Thermosol method provides several benefits compared to exhaust or batch dyeing:

1. High Production Capacity

This is a continuous process that runs at high speed (40–120 m/min), making it ideal for mills with large-volume demand.

2. Excellent Shade Uniformity

Since the dye liquor is padded evenly and heat fixation is controlled precisely, shade variation is minimal.

3. Lower Water Consumption

Unlike exhaust dyeing, Thermosol uses very little water, reducing:

• Water cost
• Effluent load
• Treatment requirements

4. Good Fastness Properties

Thermofixation ensures:

• Good wash fastness
• High rubbing fastness
• Excellent sublimation fastness

5. Suitable for Blended Fabrics

PC fabrics can be dyed continuously using Thermosol followed by reactive dyeing for cotton.

6. Eco-friendly Option

Low effluent, fewer chemicals, and better energy utilization make Thermosol more sustainable.

 

2. Step-by-Step Thermosol Dyeing Process

The full Thermosol workflow includes several stages:

 

Step 1: Pre-Treatment

Before dyeing, polyester fabric must be properly prepared.

Includes:

• Scouring
• Heat setting
• Drying

Purpose:

• Remove oils, wax, sizing chemicals
• Maintain dimensional stability
• Ensure uniform dye penetration

 

Step 2: Padding (Dye Application)

The fabric passes through a dye liquor containing:

• Disperse dyes
• Dispersing agent
• Wetting agent
• Anti-migration agent

Key Point:

Achieve 65–75% pick-up depending on fabric type.

Padding ensures even dye application across the fabric width.

 

Step 3: Drying

After padding, fabric is dried at 100–120°C to remove moisture.

Why drying is important?

• Moisture interferes with thermofixation
• Ensures sharp, consistent shades

 

Step 4: Thermofixation (Thermosol Stage)

This is the core of the process.
The fabric is heated at 190–210°C for 60–90 seconds.

What happens here?

• Polyester fiber swells
• Dye molecules diffuse inside the fiber
• Strong dye-fiber bond forms

This step determines color depth, uniformity, and fastness.

 

Step 5: Cooling

After thermofixation, the fabric must cool gradually to prevent:

• Shade change
• Sublimation
• Fabric distortion

 

Step 6: Washing / Soaping

Washing removes:

• Unfixed disperse dyes
• Surface residues
• Padding chemicals

Washing temperature:

60–70°C with detergent and dispersing agent.

Optional:

Reduction clearing may be performed for deeper shades.

 

Step 7: Final Finishing

Finishing includes:

• Softening
• Stenter finishing
• Heat setting (optional)
• Packing

Finishing ensures:

• Proper hand feel
• Dimensional stability
• Final appearance

 

3. Key Parameters for Thermosol Dyeing

Controlling parameters is essential for consistent results.

 

1. Pick-Up Percentage

• Ideal: 65–75%

Too low → Light shade
Too high → Migration, uneven dyeing

 

2. Drying Temperature

• 100–120°C

Overdrying may prevent dye penetration.
Underdrying causes poor fixation.

 

3. Thermofixation Temperature

• 190–210°C

Lower temp → Poor shade depth
Higher temp → Sublimation / shade shift

 

4. Thermofixation Time

• 60–90 seconds

Short time → Incomplete dyeing
Long time → Fabric yellowing

 

5. pH of Padding Liquor

• pH 4.5–5.5

Maintains dye stability and prevents hydrolysis.

 

6. Dye Solubility & Dispersion

• Ensure proper dispersion at 60–70°C
• Avoid dye agglomeration

 

7. Machine Parameters

• Line speed: 40–120 m/min
• Pressure of pad rollers
• Temperature uniformity in chambers

 

Common Problems in Thermosol Dyeing & Their Remedies

Defect	Cause	Solution
Shade variation	Uneven pick-up	Maintain roller pressure
Patchiness	Poor dye dispersion	Add dispersing agents
Sublimation	Excess temperature	Keep within 190–205°C
Barre effect	Fabric GSM/yarn variation	Pre-assess lot uniformity
Poor fastness	Low thermofixation time	Maintain required dwell time

 

Conclusion

The Thermosol dyeing process is a high-speed, efficient, and eco-friendly method widely used in modern polyester dye houses. With proper control of padding, drying, thermofixation, and washing parameters, mills can achieve:

• Excellent shade consistency
• Strong fastness properties
• Minimal re-dyeing
• Lower production cost

Because of these advantages, Thermosol remains one of the most powerful continuous dyeing technologies for polyester fabrics.