Dyeing of Cotton Fabric with Direct Dyes

Aim: Dyeing of cotton fabric with Direct Dye

Direct dyes:

Direct dyes are called as substantive dyes because of their excellent substantitvity for cellulosic textile materials like cotton and viscose rayon

Classification of Direct Dyes:

• Class A: Self levelling dyes
• Class B: Salt controllable dyes
• Class C: Temperature Controllable Dyes

How to dye cotton fabric with direct dyes?

The dyeing process involve 2 process:

• Preparation of dye bath
• Dyeing

Preparation of dye bath:

The dye is dissolved by pasting it with small amount of water and soda ash. Boiling water is the added to the paste with constant stirring. Stock solutions (concentrate solution as usually prepared and the required volume of this solution is taken for dyeing.

Dyeing:

The dye bath is set with required volume of the stock solution of dye, 0.5 to 1% soda ash and water to make the desired M:L ratio. Then the processed material is entered in the dye bath at 40°C and dyeing is carried out for 15 to 20 minutes. The required amount of common salt is added in even number of installments at intervals of 10 to 15 minutes. The salt varies between 5 to 20% on weight of material for light to heavy shade. The temperature of dye bath is slowly raised to boil and is continued as this temperature for the period of 45 to 60 min and then it is cool for 15 to 20 minutes for better exhaustion. The goods are then removed from dye solution, squeezed and dried and after treatment in the solution of dye fixing agent after precise drying stage.

Recipe:

• Direct dye stuff- X% (owf)
• Soda ash- 0.5 to 1 % (owf)

• Common salt-

       -5% (owf) for light shades
       -10% (owf) for medium shades
       -20% (owf) for dark shades

• Temperature- Boil
• Time- 45 to 60 min

Generally we use winch and jigger for fabric dyeing.

After treatment of direct dyes good:

Direct dyes have poor drying and washing fastness. Therefore, to  improve the fastness properties after treatment based on principle like increasing molecular weight of dye and thus decreasing their solubility after dyeing.

Treatment with metallic salts:

• Treatment with copper salts
• Treatment with chromium compounds
• Treatment with formaldehyde
• Treatment with cationic dye fixing agent
• Topping with basic dyes
• Diazotization and development of direct dyes.