The direct dye is the class of dyestuff which is used directly to the substrate in the alkaline or neutral bath. They create full shapes on linen and cotton without mordanting and can also be useful to silk, wool or rayon. It gives bright colors but exhibits poor wash.
Direct dyes are water soluble anionic dyes and retain sulphonic acid groups in structure.
This dyes are superior to others in terms of cost, better light fastness, ease of application, shorter dye cycle, low cost of auxiliaries, remarkably lesser use of water and much lower salt level in effluent.
Another name for Direct Dyes is Substantive dyes which are usually economical and easily applied, and they can yield bright colors. Direct dye used in a process in which dye molecules are attracted by physical forces at the molecular level to the textile. Higher the substantive force greater the attraction of the dyes for the fiber.
The direct dyes are sensitive to acid, and the addition of acid can make the direct dyes deposit. After dyeing, if we treat them with the fixing agent, organic acid, etc., we can improve the fastness.
