Printing of Cotton (Vat Dye)

      ⇨     Vat dyes have an outstanding fastness to external agencies, like light, washing, bleaching,  rubbing, perspiration, etc.

⇨    Therefore, vat dyes are used for shirting, window curtains, sarees, casement cloth, etc.

⇨ They can be classified into three distinct chemical groups: indigoid vat dyes, anthraquinonoid vat dyes, and sulfurized vat dyes.

⇨   Vat dyes are forming leuco compounds with a reducing agent due to reduction, which are soluble in water, and the parent colour can be generated by oxidation.

⇨     Vat dyes (indigo) can be printed by the glucose and hydrosulphite process by direct style of printing.

⇨     Glucose Process:

●       The fabric is padded with a 25% solution of glucose, dried, and printed with indigo (vat dye) with printing paste prepared under:

Ingredients	Quantity (Parts)
Indigo (vat dye)	50
Caustic soda (70˚Tw)	240
Water	260
Gum Arabic paste	450
Total	1000

●       After printing and drying, the fabric is steamed at 100°C in air-free moist steam for a few minutes.

●       Steamed fabric is passed through the solution for 15 minutes for oxidizing the dye as prepared as follows:

Ingredients	Quantity (Parts)
Sodium bicarbonate	20
Ammonium sulphate	10
Total (adjusted with water)	1000

●       Finally, fabric is washed, soaped, and dried.

 

⇨     Hydrosulphite Process:

●       The fabric is printed with indigo (vat dye) with printing paste prepared as under:

Ingredients	Quantity (Parts)
Indigo (vat dye)	150
Alkaline thickening	350
Formosul	80
Alkaline thickening	420
Total	1000

●       After printing and drying, the fabric is steamed at 102°C for 2–3 minutes in a Rapid ager.

●       Steamed fabric is oxidized in a chrome bath.

●       Finally, fabric is washed, soaped, and dried.

●       Alkaline thickening is prepared by mixing 30 parts maize paste and 100 parts British gum paste with 870 parts caustic soda (77˚Tw)

 

⇨     Potash Rongalite Method: (for anthraquinonoid vat dyes)

●       This is the most popular method for printing the vat dyes.

●       The fabric is printed with vat dye by preparing printing paste as under:

Ingredients	Quantity (Parts)
Vat dye	200
Glycerine	50
Solution Salt B	30
Starch-tragacanth paste	500
Potassium carbonate	120
Rongalite C	100
Total	1000

●       After printing, the fabric is dried as quickly as possible and steamed for 5–10 minutes in air-free moist steam at 100–102°C.

●       Steamed fabric is rinsed and then oxidized at 50°C for 2–5 minutes in a solution containing:

Ingredients	Quantity (Parts)
Sodium bicarbonate	2
Acetic acid	5
Total (adjusted with water)	1000

●       Finally, the fabric is washed, soaped at a 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