Cold Pad Batch (CPB): A Sustainable Dyeing Process for Woven and Knit Industry

Mazharul Islam
Sr. Executive (Solid Dyeing)
M.Sc. in Textile Engineering (1st Semester)
B.Sc. In Textile Engineering (PTEC Affiliated BUTex)
Email: [email protected]

Cold Pad Batch (CPB) Dyeing:
Cold Pad Batch Dyeing is one of the widely used semi-continuous dyeing process. It is mainly used in the dyeing of cellulosic fiber like cotton or viscose (knit and woven fabric) with reactive dyes. Now a days this process widely used in our Woven dyeing industry and it is a development process for Knit dyeing industry in Bangladesh. It is primarily a cold method where the dyeing temperature is 20-25°C and use Cold to Medium Brand Reactive Dyes, and so it is called Cold Pad Batch (CPB) Dyeing. A cooling system is used for cooling the Dye liquid and bath also. Cold Pad batch dyeing is a process that offers some unique advantages.

This dyeing process has gained wide acceptance due to the following reasons:

1. Maximum color yield as compared to other methods.
2. Less requirement of Energy, Water and Chemical since fixation is carried out at room temperature.
3. Cost effective Dyeing Method.
4. Good levelness of dyeing.
5. Longer yardages possible to dye.
6. Elimination of salt during dyeing. (100% Salt Free Dyeing)
7. Less impact on environmental pollution.

Compare with others dyeing (knit or woven) minimize: (source: from BENINGER web, Benninger KÜSTERS Dyepad)

• 100% Salt Free.
• Water (-75%) (low bath ratio)
• Energy (-77%).
• Carbon footprint (-78%).
• Cost (-32%).

Drawback of this process:
Every process has some drawbacks and it has also:

• Sometime listing problem found.
• Sometime tailing problem found.
• Unevenness due to uneven pretreatment

Which Fabric is suitable for CPB (Cold Pad Batch) Dyeing? List given below:

1. 100% Cotton.
2. Cotton + Spandex.
3. Cotton Viscose Blend.
4. 100% Viscose.
5. Linen.
6. Linen Cotton Blend.
7. Linen Viscose Blend.
8. Tensile.

General Parameter of CPB Machine:

• Machine Speed = 40-50 m/min
• Padder Pressure (N/mm or Bar) L-M-R = 20-30-20 or 1.2-1.5-1.2
• Dye Bath Level= 25 Ltr or 50 Ltr
• Immersion time= 1.5 sec
• Machine Utility= 5.5 KW
• Pick Up %= for Cotton 55-70% & for Viscose 85-95% or more, varies depend on Fabric GSM.

A Typical Recipe for CPB Dyeing:
Here color and chemical (alkali) are prepared separately into separate tank which prevent hydrolysis of dyes molecule. At the time of padding both color and chemical liquid are mixed at dye bath (Temp around 20-25°C). Mixing ratio is Color : Chemical = 4 : 1. This mixing process is done by a dossing pump.

Color Liquid:

• Leva Amber CAN              = 9.00 g/l
• Leva Fast Red CA              = 0.6 g/l
• Leva Blue CA                      = 15.20 g/l
• Dekol 1097                          = 2 g/l
• Leonil EHC                           = 2 g/l
• Urea                                      = 40 g/l

Chemical Liquid (Alkali):

• Soda Ash (Na2CO3 )        = 20 g/l
• Caustic Soda- (NaOH)     = 3 or 6 g/l (7.5ml/l or 15ml/l for 36°Be)

If we need 100 Ltr Liquid for Dyeing, follow the Color and Chemical ratio 4 : 1 to make Color and Chemical separately, and so we make 80 Ltr of Color and 20 Ltr of Chemical for dyeing.

Here Dekol-1097 acts as a Leveling & Sequestering Agent and Leonil EHC acts as a Wetting agent, and Urea used to keep the Dye bath cool and it acts as a Hygroscopic Agent. Here (Soda Ash & Caustic) – Chemical (Alkali) is used as a Fixing agent and also control the pH of Dye Bath.

Cold Pad Batch (CPB) Process Flow Chart:

Batcher/Plate (fabric feed)

↓

J-Box (not Necessary)

↓

Cooling Drums

↓

Application Dyeing in Dye Bath

↓

Squeeze by Padder

↓

Collecting Fabric in Batcher

↓

Rotation (for Color Fixation)

↓

Washing

↓

Shade Check

↓

Transfer to Finishing

1. Firstly the RFD (Ready for Dyeing) Fabric is introduced with Cooling Drum, it is a cooling system here the fabric is cooled down.
2. Then the RFD Fabric is introduced with pre-mixed dye liquor at Dye Bath. Here Dye Bath Temp around 20-25°C and so it is called Cold Pad Batch (CPB) Dyeing. A cooling system is used for cooling the Dye liquid and bath also.
3. Then it is passed through Padder. The padder effectively forces the dyestuff into the fabric. In the stage excess dye solution is also removed.
4. After removal of excess dye stuff the fabric is collected in Batcher. The batches are generally enclosed by plastic films. This prevents absorption of carbon dioxide and water evaporation.
5. After removing batcher from dyeing machine, it is placed at Rotation Point. It takes around 8-14 hours (Time depends on Shade). Finally as the reaction is complete the fabrics are washed.

References:

1. https://www.benningergroup.com
2. Textile Journal-Different Dyeing Process.
3. http://www.geocities.ws/dyes_pigments/continuous-dyeing-process.html

You may also like:

1. Salt Free Dyeing of Cotton Fabric with Reactive Dyes
2. Salt and Alkali Free Reactive Dyeing on Cotton Fabric
3. Sustainable Dyeing Process in Textile 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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