Important things of vat dyeing process

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Important things of vat dyeing process:

Properties of vat dyes:

The benefits of VAT dye are discussed below:

1. Vat dye is insoluble in water and cannot be applied directly to textile products.

2. It is soluble in a toxic state. It is usually disinfected by sodium hydrosulphide and sodium hydroxide.

3. This dye is mainly used for cellulosic fiber dyeing. The PH of protein fiber dye is to be controlled.

4. Wet fastness and lightfastness of this dye are very good.

5. It provides shades of different colors.

6. Oxidation is required for the development of color.

7. The price of this dye is relatively high.

8. This dye is very bright and ripe.

9. This dye is very complex to make.

10. Rubbing fastness of this dye is not good.


The process by which Insoluble Vat Dye is variously converted to soluble form is called Vatting.

Vat dye is insoluble in water. To dissolve it, the dyes are first disintegrated converted into a leuco compound, which is then dissolved in water with the help of alkali (NaOH). Vatting is the conversion of vat dye (insoluble) into sodium salt of leuko compound (soluble) which is soluble in water.


Advantage of the modern method of vat-dying over the older one:

(1) Reduced bath can be made at any time as per requirement.

(2) The wastage of indigo is not high here.

(3) Free from any kind of interference due to reaction products.

(4) Acid souring is required to remove lime deposit for the old process. But in the modern process, it is not necessary.

(5) It is a fast process and perfect standardization is possible here.

After treatment of vat dye:

Important things of vat dyeing process. After removing the product from the dye bath and squeezing it well and hanging it in the air for 10 to 15 minutes, it becomes oxidized and the color appears in the product.

After treatment, the product is treated with 2% soap and 3% soda at 70°C for 30 minutes. This removes the loose color of the fabric and increases the durability of the dye. Later the cloth is dried.

Vat dyes stripping process :

Defective dyeing is caused by uneven application of leuko vat dye by textile products. This problem can be solved by mixing a small amount of leveling agent, sodium hydroxide, sodium hydrosulphide in a container and re-vatting the cloth in that bath. Increasing the amount of leveling agent increases the amount of stripping. In this method, partial stripping occurs. Re-dyeing by quantitative like vat dye is required in the new bath to get the desired shade.

If complete stripping is required, the dye is completely removed from the fabric by treatment at 90°C for 45 minutes with 5 g / liter sodium hydrosulfide and 16 g / liter of caustic soda

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