According to the chemical structure classification, acid dyes can be divided into azo, anthraquinone, triarylmethane and other categories.
①Azo type: single and double azo dyes, mainly light colors (yellow, orange, red, purple, blue), the majority of varieties;
②Anthraquinone type: Monoanthraquinone is the main type, mainly dark (purple, blue, green) varieties occupy the second place, the best fastness to sunlight
③ Triarylmethane type: bright color, high intensity, mainly purple, blue and green, and the worst fastness to sunlight.
Acid dyes are divided into strong acid, weak acid, acid medium, acid complex dyes, etc. according to their chemical structure and dyeing conditions.
Strong acid dye: an acid dye developed in the earliest period, which requires dyeing in a strong acid dye bath. It has a simple molecular structure, low molecular weight, and contains sulfonic acid groups or carboxyl groups. Strong water-based, weak hydrophobic, good water-solubility, low affinity to wool, can transfer dye on wool, dye evenly, so it is also called acid level dye, but the shade is not deep, and the wash fastness is poor, and The wool is damaged during dyeing, and the wool feels poor after dyeing. It needs to be dyed in a strong acid bath to obtain a high dyeing rate, bright color, suitable for dyeing light to medium colors, mainly used for wool dyeing.
Weak acid dyes: Weak acid dyes are produced in strong acid dyes by increasing molecular weight, introducing groups such as arylsulfone groups, or introducing long carbon chains. The molecular structure is more complicated, the proportion of sulfonic acid groups in the molecule is relatively small, hydrophilicity, aggregation and solubility in aqueous solution are medium, the affinity for wool is large, the migration and level dyeing properties are slightly poor, and the wet treatment It has good fastness. It can dye wool in weak acidic medium without damage to wool. The shade is darker and the fastness has been improved, but the levelness is not good.
Acid mordant dyes: acid dyes that form metal complexes on fabrics after being treated with certain metal salts (such as chromium salts, copper salts, etc.) as mordants. The mordant procedures are more complicated, but the properties of light fastness, washing fastness and rubbing fastness are better.
Acid complex dyes: It is formed by complexing some acid dyes with metals such as chromium and cobalt. It is soluble in water and has excellent light and light resistance. Its dye precursor is similar to acid mordant dye, but in the preparation of dyes, metal atoms have been introduced into azo dye molecules, the ratio of metal atoms to dye molecules is 1: 1, so it is also called 1: 1 metal complex dye. There is no need to use mordant for dyeing. It must be dyed in a strong acid bath, which will damage the wool.
Another type of acidic complex dye molecules do not contain sulfonic acid groups, but contain hydrophilic groups such as sulfonamido groups. The ratio of metal atoms in the molecule to the dye molecule is 1: 2, so it is also called 1: 2 metal complex dye. It is dyed in a neutral or weakly acidic medium, so it is called a neutral dye, also known as a shrink-resistant acid dye. The dye has a complex structure, a large molecular weight, a small proportion of sulfonic acid groups in the molecule, and a large proportion of the hydrophobic part. Poor water solubility, high affinity for wool and other fibers, poor dye transfer and level dyeing, often dyed in a near-neutral bath, the color is not bright enough, and the fastness of ironing and wet treatment is good.