Properties of direct dyes and uses

Dye is one of the of chemicals that is close to human life, its product properties determine which is an innovation-driven industry. China textile dye is primarily reactive dyes and VAT dyes and direct dyes, and the price of direct dyes is one-tenth of reactive dyes and VAT dyes.
The pursuit of color gave birth to the synthetic dye industry, and with the birth of new textile materials, scientists have also developed disperse dyes and cationic dyes for acrylic. Different printing processes, different areas of application, developing consumer demand, a wide range of new demands on the dye, dyestuff industry is constantly develop and grow up through product innovation and technological innovation. It can be said that the modern innovation of dyestuff industry born with the original gene.

Dyes are divided into ten categories, such as reactive dyes, direct dyes and disperse dyes, etc. Theoretically, cationic dyes are special dyes for acrylic fibers, but plant often encountered poor production in dyeing with cationic dyes, mixed colors combination limited by value k, higher prices and so on. Practice has proved that the direct dye dyeing acrylic fibres at the acidic conditions, sample fabrics are bright, pure light, the depth also is ideal, meanwhile it helps factories reduce the cost of dyeing.
Direct dyes stand for a wide range of colorants that are very economical. There are three common ways to classify direct dyes: chemical structure, dyeing properties and their fastness properties.

Direct dye containing sulfonate or carboxylate salt, it dissociates into sulfonic acid or sodium carboxylate anions and cations in water. Using cationic compounds as a fixing agent, and occurs ion exchange reaction with anions of dyes on fibers, then generate salt that is slightly soluble or insoluble in water, preventing the dye dissolved in water ionization and breaking off from the fabric. Direct dyes vary widely in their fastness properties and staining effects on various fibres.

Direct dyes can apply batch dyeing methods, semi-continuous methods and continuous methods. Combined scouring and dyeing are suitable for many direct dyes. Usually, soda ash and non-ionic detergent are employed. However, dyes containing amide groups are prohibited as the reason of the risk of alkaline hydrolysis. By the way, Effect of temperature on different dyes dyeing properties are different. For dyeing rate high, good diffusion properties of direct dyes, it get most deep color at 60 - 70 ℃, while the dyeing rate decreased when the temperature is above 90 ℃.