There are varieties of acid dye, which have complete chromatography and bright color. There are sulfonic acid groups in the molecule (SO3H), which belongs to the water soluble anionic dyes. In acidic and silk strong acidic or neutral bath, hydrogen bonding will react with amide molecules of wool fiber and nylon fiber. It can also react with the amine base and produces imino ionic bonds.
Therefore, acid dyes can be widely used in the dyeing and printing of fabrics like silk, wool and chinlon. According to the dyeing properties, acid dyes can be divided into three kinds of dyes: strong acid, weak acid and neutral dye. The molecular mass of strong acid dye is comparatively small. The affinity of acid dye for fiber is low. Its directness is small. It is easy to diffusing and dyeing. Thus it has good level-dyeing property. However, the color fastness is not that satisfying when only relying to the combination of electrovalent bond and fiber.
However, the molecular mass of weak acid is relatively larger, and the affinity for fiber is big. Although it is difficult to diffuse and dye and has ordinary level-dyeing property, it can also achieve good dyeing effect by adding auxiliaries during the dyeing. It can not only combined with fiber by electrovalent bond, but also with hydrogen bond and Van Der Waals force. Thus the color fastness of it is good. It is the acid dye that commonly used.
After dyeing by the acid dye, the fabric must be washed to remove auxiliaries and dyes which didn't react. Then achieve some color fastness. Because the affinity of weak acid dye for fiber is relatively big, dyes are easy to come back to fiber during the washing, and it may affect color fastness.
The dyes easy to color such as acid brilliant scarlet F3GL, acid red 10B, acid blue 6B, acid brilliant G, acid lake blue 5GMA, acid black B, acid black BGL. Especially red, blue series dyes can hardly be repaired after stained. Thus stain proof soaping agent must be used in washing.
Because the stain proof property of acid dyes is totally different with that of reactive dyes, the stain proof soaping agent is different. Because acid dyes are anionic dyes, it can only achieve the property of stain proof by using a cationic surface active agent and a highly effective dispersant . Stain proof soaping agent should be used after the dyeing of acid dyes.