Classification of direct Dye with the basis of Applications
1.Class A ( Self Leveling ): Dye which migrate well and therefore have high leveling power.
2.Class B ( Salt controllable ): Dyes of poor leveling power where exhaustion must be brought by the controlled salt addition.
3.Class C ( Temperature Controlled ): Dyes which are not self leveling and wre highly sensitive to salt. The exhaustion of these dyes can not adequately be controlled by addition of salt alone and they require additional control of temp.
Methods of After treatment in dyeing of direct dye
1.Coupling with Di-azonium salt: Direct dye have a similar structure to the base of azoic dyes. So these dyes are to be treated nepthols as in case with azoic dyes. By this coupling system, improves the dye’s wash fastness from poor to moderate. The dyed material simply treated in a nitrous acid bath, rinsed and passed into a cold developing bath several developers are available.
m-phenylene diamine, nepthol.
2.After treatment with metallic salt: The dyed material is carried out at 70ºC for 30 minutes in a bath containing acetic acid (3% to 30%) and crystalline copper sulphate (1% to 3%) according to the depth of shade.
3.After treatment with formaldehyde : Treatment with formaldehyde (1% to 3% of a 40% solution) and 1% acetic acid at 80ºC for 30 minutes to improve the wash fastness of direct dye.
4.Cationic Fixing agent: The cationic fixing agent is adding to aqueous solution. It will also ionized and the main important agent cationic fixing agent at the direct dye.
Difference between Direct, Acid and Basic Dye
|More azo group in dye molecule
|Only one azo group in dye molecule
|Substituted amino group
|Big Molecular Size
|Small molecular size
|Smaller than direct dye
|Have direct affinity to Cellulose fiber
|Have direct affinity to protein fiber
|Have no direct affinity to protein or cellulose fiber
|Has done either acid, alkali or neutral medium
|Has done in acid medium
|Has done in neutral Medium
|Wash fastness 2-3
|Wash fastness in 2-5
|Wash fastness 4-5