Acid Dyes are a class of water-soluble dyes with acidic groups in their structure, which are dyed in acidic media. Most of the acid dyes contain sulfonic acid sodium salt, which is soluble in water, bright in color and complete in chromatogram. Mainly used for dyeing wool, silk and nylon, but also for leather, paper, ink, etc. Generally no coloring power to cellulose fibers.
Acid dyes have complete chromatograms, bright colors, and the light fastness and wet fastness vary greatly with the variety of dyes. Compared with direct dyes, acid dyes have a simple structure and lack long conjugated double bonds and a homoplanar structure, so they lack directness to cellulose fibers and cannot be used for dyeing cellulose fibers. Different types of acid dyes have different dyeing properties and different dyeing methods due to different molecular structures.
Mainly used for dyeing wool, silk and nylon, but also for leather, paper, ink, etc. Generally no coloring power to cellulose fibers.
(1) Strong acid dyes
One of the earliest developed acid dyes requires dyeing in a strong acid dye bath. Its molecular structure is simple, its molecular weight is low, it contains sulfonic acid or carboxyl groups, and it has little affinity for wool. It is uniform, so it is also called acid level dyeing dye, but the color is not deep, the washing fastness is poor, and the wool is damaged during dyeing, and the dyed wool feels poor. Such as Acid Red G (ie C.I. Acid Red 1).
(2) Weak acid dyes
In strong acid dyes, weak acid dyes are generated by increasing the molecular weight, introducing groups such as arylsulfone groups, or introducing long carbon chains. The molecular structure is more complex, and the affinity for wool is large. It can dye wool in weakly acidic medium without damage to wool. Such as weak acid brilliant blue RAW (ie C.I. acid blue 80).
(3) Acid mordant dye
Acid dyes that form metal complexes on fabrics after treatment with certain metal salts (such as chromium salts, copper salts, etc.) as mordant. Mordant procedures are more complicated, but dyes with better performance such as light fastness, washing fastness and rubbing fastness can be obtained, such as acid medium black T (ie C.I. medium black 11).
(4) Acid complex dyes
It is formed by complexing some acid dyes with metals such as chromium and cobalt. It is soluble in water, and its dyeing products have excellent lightfastness and lightfastness. Its dye parent is similar to the acid mordant dye, but when preparing the dye, the metal atom has been introduced into the azo dye molecule, and the ratio of the metal atom to the dye molecule is 1:1, so it is also called 1:1 metal complex dye. No further mordant treatment is required for staining. Such as acid complex yellow GR (ie C.I. acid yellow 99).