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Cotton Printing (Reactive Dye)

• Reactive dyes based on vinyl sulphone (SO₂-CH=CH₂) group are widely used for printing the cotton materials, like bed sheets, pillow covers, lungies etc. as this group can be fixed without steaming, and so most suitable for cottage industries.
• Vinyl sulphone dyes are fixed by padding the printed fabric through sodium silicate (about 106˚ Tw) solution.
• Dichloro (cold brand) and monochloro (hot brand) traizine dyes are fixed due to substitution reaction with the liberation of HCl

•  Direct Style:

· Reactive Dye: These are molecules that form a covalent bond with the cotton fabric molecules, and it is an anionic dye.

· Thickeners: As the reactive dye reacts with primary hydroxyl groups, gums and starches are not suitable as a thickener. Therefore, sodium alginate is the best suitable thickener for reactive dye printing. But in the case of steaming fixation, half-emulsion thickener is advisable.

·  Mild oxidizing agent: Resist Salt L (Ludigol)

· Solvent: Urea, Diethylene glycol, thiodoethylen glycol

· Hygroscopic agent: Urea, glycerine - It increases the brightness of the dye and spread the dye evenly in the paste. Assist the dye fixation and prevent aggregation of the dye.

· Weak alkali: Sodium bicarbonate (NaHCO₃) – for maintain the pH, and also helps in fixation.

·  Various methods of printing reactive dyes depends on the process used for fixation of the dye, and they are

[1]   Steaming                     [2] Baking or Thermofixing

[3] Flash-ageing                [4] Wet developing

[5] Silicate padding          [6] Air hanging

1)      Steaming Process

·         For printing the cotton with reactive dye by direct style, following paste is used:

 

Ingredients	Quantity (Parts)
Reactive Dye	50
Water	290
Urea	180
Resist Salt L	10
Sodium bicarbonate	20
Sodium alginate (6%)	450
Total	1000

·         After printing and drying, the fabric is steamed for 5 – 10 minutes in Rapid ager and for 15 – 20 minutes in a Star ager or steamed under high pressure at 130˚C for 30 seconds, then rinsed well in cold water, soaped with 2 gpl non-ionic detergent, rinsed and dried.

·         During steaming sodium bicarbonate decomposes to give alkaline conditions for fixation of the dye.

 

2)      Baking or Thermo-fixing Process

·         Urea is used in high concentration in this process.

·         Cold brand reactive dyes are fixed by using sodium bicarbonate and hot brand reactive dyes are fixed by sodium carbonate.

·         For printing the cotton with reactive dye by direct style, following paste is used:

 

Ingredients	Quantity (Parts)
Reactive Dye	50
Water	375
Urea	200
Resist Salt L	10
Sodium carbonate (hot brand) Sodium bicarbonate (cold brand)	15
Sodium alginate (6%)	350
Total	1000

·         After printing and dyeing, the fabric is baked or thermo fixed at 150˚C for 5 minutes, soaped with non-ionic detergent at boil, rinsed and dried.

 

3)       Flash-ageing Process

·         In this process, the fabric is printed with a paste which does not contain alkali, and then padded with an alkaline solution.

·         After padding the fabric is steamed in the wet condition at 140˚C for 30 seconds, which is known as flash-ageing.

·         For printing the cotton with reactive dye by direct style, following paste is used:

 

Ingredients	Quantity (Parts)
Reactive Dye	50
Water	480
Urea	100
Resist Salt L	10
Sodium alginate (6%)	360
Total	1000

·         After printing and drying, the fabric is padded with a solution containing:

Ingredients	Quantity (Parts)
Caustic soda (70˚Tw)	60
Sodium carbonate	150
Potassium carbonate	50
Common salt	100
Solution made with water	1000

·         After padding, the fabric is steamed in the wet condition at 140˚C for 30 seconds by passing through Festoon ager.

·         The fabric is then washed to remove alkali, soaped with non-ionic detergent, washed and dried.

 

4)      Wet Development

·         In this process, after printing fabric is passed through hot alkaline solution at 95˚ to 98˚C for 15 seconds, and steaming is not done.

·         This process is most suitable for viscose rayon fabrics.

·         This process can fix 50% more colour than normal steaming process.

·         For printing the cotton with reactive dye by direct style, following paste is used:

 

Ingredients	Quantity (Parts)
Reactive Dye	50
Water	240
Urea	200
Resist Salt L	10
Sodium alginate (6%)	500
Total	1000

·         After printing and drying, the fabric is steamed for 5 minutes at 100 – 102˚C, and then pass through a solution containing:

Ingredients	Quantity (Parts)
Caustic soda (66˚Tw)	60
Sodium carbonate	100
Sodium silicate	20
Common salt	150
Solution made with water	1000

·         After passing the fabric from above solution, fabric is rinsed with cold water first and then with hot water, soaped with non-ionic detergent, rinsed and dried.

 

5)      Silicate Padding (Pad-Batch) Process

·         Vinyl sulphone based reactive dyes are majorly printed using this process. The process is most suitable for cottage industries, as the fixation of dye is done by padding the printed fabric through sodium silicate solution.

·         The fabric is printed with the paste prepared as in Flash-ageing process, and after drying the fabric is padded though 106˚ Tw sodium silicate solution at pH 11.4 – 12.

·         After padding the fabric is batched and stored for 12 – 14 hours and then rinsed, soaped with non-ionic detergent at boil, rinsed and dried.

 

6)      Air Hanging Process

·         For printing of mercerized cotton or rayon with cold brand reactive dye, this process is mostly applied.

·         The fabric is padded with 2% sodium carbonate and dried.

·         After padding the fabric is printed with the paste prepared as in Steaming process, but without sodium bicarbonate.

·         After printing, the fabric is dried by hanging in air for several hours in warm, humid atmosphere.

·         Finally, fabric is rinsed, soaped with non-ionic detergent at boil, rinsed and dried.

 

ð  White Discharge style:

·    For discharge printing, cotton is dye with some selected procion dyes, which can be discharged easily, and give good whites on the ground.

·    This style for reactive dyed ground is limited for specific application and so, it is not popular.

·     The fabric is dyed with a dischargeable reactive dye (dischargeability rating 4 – 5) is taken and printed with discharging agent for white discharge printing.

·         Discharging agent: Rongalite C (Sodium Sulphoxylate Formaldehyde) (NaHSO₂.CH₂O.2H₂O) acts as discharging agent. It is not a powerful reducing agent at room temperature. It is dissolved in cold water, and then boiled to separate formaldehyde and sodium sulphoxylate, and thus separated sodium sulphoxylate is the powerful reducing agent.

·       Zinc oxide: for obtaining better white

·   For obtaining white discharge effect on the cotton fabric dyed with reactive dye by discharge style, following paste is used:-

 

Ingredients	Quantity (Parts)
Rongalite C	150
Cold water	50
Gum-tragacanth thickener paste	625
ZnO	125
Sodium carbonate	50
Total	1000

 

·         After printing and drying, the fabric is steamed for 15 minutes in rapid ager at 100 – 102˚C, rinsed well and dried. 

 

ð  Colour Discharge style:

·    The fabric is dyed with a dischargeable reactive dye (dischargeability rating 4 – 5) is taken and printed with discharging agent for Colour discharge printing.

· Discharging agent: Rongalite C (Sodium Sulphoxylate Formaldehyde) (NaHSO₂.CH₂O.2H₂O) acts as discharging agent. It is not a powerful reducing agent at room temperature. It is dissolved in cold water, and then boiled to separate formaldehyde and sodium sulphoxylate, and thus separated sodium sulphoxylate is the powerful reducing agent.

·      Zinc oxide: for obtaining better white

·   For obtaining Colour discharge effect on the cotton fabric dyed with reactive dye by discharge style, following paste is used:-

 

Ingredients	Quantity (Parts)
Vat Dye Rongalite C	50 100
Cold water	50
Gum-tragacanth thickener paste	625
ZnO	125
Sodium carbonate	50
Total	1000

 

·      After printing and drying, the fabric is steamed for 15 minutes in rapid ager at 100 – 102˚C, rinsed well and dried.

 

ð  White Resist style:

·         Resist style is more popular than the discharged style on reactive dye ground.

·         Resisting agent: Citric acid is used as a resisting agent.

·      As acidic environment is not suitable for development of reactive dye, and so, where citric acid is present reactive dye will not develop. 

·       For obtaining white resist effect on the cotton fabric by resist style, following paste is used:-

 

Ingredients	Quantity (Parts)
Citric acid	50
Water	350
Acid-resistant thickener	600
Total	1000

·         After printing and drying, the fabric is padded with a solution containing:

Ingredients	Quantity (Parts)
Reactive dye (Remazol)	50
Resist salt L	10
Water (hot)	360
Sodium bicarbonate (3%)	500
Acid-resistant thickener	80
Total	1000

·        After padding and drying, the fabric is steamed for 10 minutes, rinsed, soaped with non-ionic detergent, rinsed and dried.

 

ð  Colour Resist style:

·         Coloured resist on reactive dyed ground can be obtained with solublised vat dyes.

·         The fabric is first padded with the solution shown below:

Ingredients	Quantity (Parts)
Reactive dye (Remazol)	30
Sodium chlorate	10
Water (hot)	300
Lactic acid	2
Gum-tragacanth thickener	50
Total (adjusted with water)	1000

·         Padded fabric is printed with following paste:

Ingredients	Quantity (Parts)
Solublised vat dye	50
Water	375
Glycine A	40
Citric acid	100
Starch-tragacanth thickener	400
Ammonium vanadate	20
Alum	15
Total	1000

·         After printing, the fabric is quickly dried, steamed for developing the solublised vat dye, and then padded through the solution containing:

Ingredients	Quantity (Parts)
Caustic soda (70˚Tw)	20
Glauber’s salt	200
Common salt	100
Total (adjusted with water)	1000

          ·  Padded fabric is then steamed in wet condition at 140˚C for 30 seconds, rinsed, soaped with                   non-ionic detergent at boil, rinsed and dried.

References:

Sr. No.	Title of Book	Author	Publication with place, year and ISBN
1	Technology of Printing Vol – IV	Dr V.A. Shehnai	Sevak Publications, Mumbai 1990
2	Textile Printing	L.W.C. Miles	Society of Dyers and Colourists, 1981, ISBN: 9780901956330
3	Introduction to Textile Printing	W. Clarke	Wood-head Publishing Ltd., Cambridge, ISBN: 9781855739949
4	Technology of Printing	R. S. Prayag	Shree J. Printers, Pune
5	An Introduction to Textile Coloration: Principles and Practices	Roger H. Wardman	‎Wiley, 1st edition ISBN: 978-1119121565