Acid dyes are classified into strong acidity, weak acidity, acid medium, and acid complex dye according to their chemical structure and dyeing conditions.
Strong acid dye
The earliest developed acid dye requires dyeing in a strong acid dye bath. Its molecular structure is simple, its molecular weight is low, it contains sulfonic acid groups or carboxyl groups, it has little affinity for wool, and it can be evenly dyed on wool. It is evenly called, so it is also called acid leveling dye, but the color is not deep, the washing fastness is poor, and the wool is damaged when dyed, and the dyed wool has a poor hand feeling. Such as acid red G (ie C.I. Acid Red 1).
Weak acid dye
A weak acid dye is formed in a strong acid dye by a method of increasing a molecular weight, introducing a group such as an arylsulfone group, or introducing a long carbon chain. The molecular structure is more complicated, and the affinity for wool is relatively large. It can dye wool in weakly acidic medium, has no damage to wool, has darker shade, and has improved fastness but uneven dyeing. Such as weak acid blue RAW (ie C.I. Acid Blue 80).
After treatment with a certain metal salt (such as a chromium salt, a copper salt, etc.) as a mordant, an acid dye of a metal complex is formed on the fabric. The mord dyeing procedure is more complicated, but it can obtain dyeing products with better performance such as light fastness, washing resistance and rubbing fastness, such as acidic medium black T (ie C.I. medium black 11).
Acid complex dye
It is formed by complexing certain acid dyes with metals such as chromium and cobalt. It is soluble in water, and its dyed products are light fast and have excellent light resistance. Its dye precursor is similar to the acid medium dye, but in the preparation of the dye, the metal atom has been introduced into the azo dye molecule, and the metal atom to dye molecule ratio is 1:1, so it is also called 1:1 metal complex dye. It is not necessary to use mordant for dyeing. Such as acidic complex yellow GR (ie C.I. Acid Yellow 99).
Another type of acid complex dye molecule does not contain a sulfonic acid group, but contains a hydrophilic group such as a sulfonylamino group. The ratio of the metal atom to the dye molecule in the molecule is 1:2, so it is also called a 1:2 metal complex dye. It is dyed in neutral or weakly acidic media and is therefore called a neutral dye. Such as neutral gray 2BL (ie C.I. Acid Black 60).
Acid dyes are azo type, hydrazine type, triarylmethane type, etc., but most of them belong to azo dyes. The production of acid complex dyes is similar to that of general dyes, but it must be increased by a one-step process of complexing with metals, such as neutral ash 2BL, first diazotized from 2-aminophenol-4-sulfonamide, and 1-acetamido-7. - Naphthol coupling, then complexed with sodium chromite sodium.