Discharge style printing by vat dye:
Table of Contents
Introduction:
White or color discharge effect can be created on the fabric dyed by VAT dye. This is done by simple reduction or oxidation. In the case of white discharge, it is convenient to use both reduction and oxidation methods. However, in case of color discharge, it is dangerous as cotton is likely to be oxidized. https://bdfabric.com/printing-of-cotton-fabrics-with-vat-dyes/
it can be done in two ways. eg
(1) White discharge method
(2) Color discharge method:
(1) Discharge style printing by vat dye-White discharge method:
It can be divided into two types. eg,
(a) White discharge by reduction method
(b) White discharge by oxidation method
(a) White discharge by reduction method:
In this reduction method reducing substances like Rongalite C, Formosol G, Zinc Dust, Glucose, etc. are used. However, Rongalite C (sodium oxalate formaldehyde) is more commonly used.
Recipe:
British gum paste → 450 grams
Zinc oxide (50% aqueous solution) → 150 grams
Titanium dioxide (50% aqueous solution) → 100 grams
Water → 50 grams
Rongalite C → 350 grams
Licotrop W → 30 grams
Glycerin → 30 grams
Anthraquinone paste (30%) → 40 grams
Total → 1000 grams printing paste
Fabrics dyed by VAT dye are printed with the mentioned printing paste. Then it is dried. The cloth is steamed for 5minutes at a temperature of 100°C – 102°C. The cloth is then washed in an open condition with boiling temperature in a solution of 1-2% sodium hydroxide. The cloth is then washed in cold water, washed in hot soapy water, and dried, and the printed area becomes white.
(b) White discharge by oxidation method:
In this method, it is easy to remove the color from indigoid vat dyed fabric. However, this method must be careful. This is because excessive oxidation can ruin the cotton fabric.
Recipe:
Potassium dichromate → 180 grams
Hot water → 275 grams
Potassium carbonate → 85 grams
Fried starch → 280 grams
Water (heated and cooled) → 200 grams
Total → 1000 grams printing paste.
Fabrics dyed by VAT dye are printed by the mentioned printing paste. The cloth is then dried in a mixture of 50 g/liter of sulfuric acid and 50 g/liter of oxalic acid at a temperature of 50°C to 60°C for 30 to 40 seconds and then washed and dried. As a result, the printed part of the cloth is observed to be white.
(2) Discharge style printing by vat dye-Color discharge method:
Azoic dyes are best for color discharge on fabrics dyed by VAT dyes. In addition, solubilized VAT dyes are used to replace VAT dyes. The color paste of the color discharge replaced by solubilized VAT is made by the following materials.
Recipe:
Solubilized VAT Dye → 30 – 100 grams
Ethyl glycol → 25 grams
Diethyl tartrate → 60 grams
Potassium chromate → 150 grams
Water → 125-195 grams
Potassium ferrocyanide → 60 grams
Neutral Thickener (Starch / Gum Tregakanth) → 200 grams
Ammonium Hydroxide (25%) → 10 grams
Total → 1000 grams printing paste
The printing is done on the fabric dyed by VAT dye with the mentioned printing paste. After drying, the cloth is steamed at 100°C to 102°C in Rapid ager for 5 minutes, then washed in soapy water and dried. As a result, the color of solubilized vat dye will bloom in the printing area.
