Acid dyestuffs are divided into strong acid, weak acid, acid mordant, acid complex dyestuffs and so on according to their chemical structure and dyeing conditions.1. Strong Acid Dyestuffs
The earliest developed acid dyes are required to be dyed in a strong acidic dyeing bath, with simple molecular structure, low molecular weight, containing sulfonic acid or carboxylic acid group, not much affinity to wool, and can shift evenly on wool, dyeing evenly, so it is also called acidic level dyeing dyes, but the color light is not deep, the fastness to washing is poorer, and the dyeing is damaging to the wool, and the handfeel of the wool after dyeing is poorer. Such as acid red G (i.e. C.I. acid red 1).
2、Weak acid dyes
In the strong acidic dyes by increasing the molecular star, the introduction of alum base and other groups or the introduction of long carbon chains and other methods that generate weak acidic dyes. The molecular structure is more complex, the affinity for wool is greater, can be dyed in a weak acidic medium wool, no damage to wool, deeper color light, firmness improved, but not evenly dyed. Such as weak acid brilliant blue RAW (i.e. C.. Acid blue 80).
3、Acidic Mordant Dyes
With certain metal salts (such as chromium salt, copper salt, etc.) for the mordant treatment, the formation of metal complexes on the fabric of acid dyes. Mordanting procedure is more complicated, but can get sunlight resistance, washing resistance, friction fastness and other properties of the dye, such as acid medium black T (i.e. C.I. medium black 11).
4、Acid complex dye
It is made by complexing certain acid dyes with chromium, cobalt and other metals. It is soluble in water and has excellent sunlight and light resistance. Its dye mother and acidic mordant dyes are similar, but in the preparation of dyes, metal atoms have been introduced into the azo dye molecules, metal atoms and dye molecules than 1:1, so it is also known as 1:1 metal complex dyes. It is also called 1:1 metal complex dye. It does not need to be treated with mordant when dyeing. Such as acid complex yellow GR (i.e. C.I. acid yellow 99).
Another type of acid complex dyes do not contain sulfonic acid group in the molecule, but contain hydrophilic groups such as sulfonylamino group, the ratio of metal atoms in the molecule and dye molecule is 1:2, so it is also called 1:2 metal complex dyes. It dyes in neutral or weakly acidic medium, so it is called neutral dye. Such as neutral gray 2BL (i.e. C.I. Acid Black 60).
Acid dyes are azo, anthracene, triarylmethane and so on, but most of them are azo dyes. The production of acid complex dyes is similar to that of general dyes, but it is necessary to add one step to the process of complexing with metals, for example, Neutral Gray 2BL, which is first diazotized by 2-aminophenol-4-sulfonamide, coupled with 1-acetylamino-7-prohibited phenol, and then complexed with chromium sodium salicylate.