Classification by chemical structure
Divided into: azo dyes, anthraquinone dyes, aromatic methane dyes, indigo dyes, sulfur dyes, phthalocyanine dyes, nitro and nitroso dyes, in addition to dyes of other structural types, such as methine and polymethine dyes, stilbene dyes and various heterocyclic dyes.
Classification by application performance
Divided into: direct dyes, acid dyes, cationic dyes, reactive dyes, insoluble azo dyes, disperse dyes, vat dyes, sulfur dyes, condensation dyes, fluorescent brighteners, in addition, there are oxidative dyes for textiles (such as aniline black), solvent dyes, polypropylene dyes and food pigments for food.
Introduction to various dyes
| Dye name | Structural properties and characteristics | Dyeing objects and methods |
| Direct dyes | Direct dyes are a type of water-soluble anionic dyes. Most dye molecules contain sulfonic acid groups, while some have carboxyl groups. The dye molecules are bonded to cellulose molecules by van der Waals forces and hydrogen bonds. | Direct dyes are mainly used for dyeing cellulose fibers, and can also be used for dyeing silk, paper, and leather. During dyeing, the dye directly dyes the fiber in the dye solution and is adsorbed on the fiber through van der Waals forces and hydrogen bonds. |
| Acid dyes | Acid dyes are a type of water-soluble anionic dyes. The dye molecules contain acidic groups such as sulfonic acid and carboxyl groups, usually in the form of sodium salts. In the acidic dye bath, they can be ionically bonded with the amino groups in the protein fiber molecules, so they are called acid dyes. | Commonly used for dyeing silk, wool, polyamide fibers and leather. Acid dyes dye fibers through their own affinity and bond with fibers through ionic bonds; acid mordant dyes have similar dyeing conditions to acid dyes, but require the action of certain metal salts to form chelates on the fibers to obtain good wash resistance; acid mordant dyes, some acid dyes have chelated metal ions in their molecules, have a low tendency to hydrolyze, and have good color fastness |
| Cationic dyes | Cationic dyes are soluble in water and are in a cationic state. Early dye molecules have basic groups such as amino groups and often exist in the form of acid salts. | Mainly used for dyeing polyacrylonitrile fibers, they can combine with carboxyl anions in protein fiber molecules such as silk in the form of salt bonds during dyeing. |
| Reactive dyes | Reactive dyes are also called reactive dyes. This type of dye contains active groups in its molecular structure, which can covalently bond with the hydroxyl and amino groups in the fiber molecules during dyeing and firmly dye the fibers. | Reactive dyes are mainly used for dyeing and printing cellulose fiber textiles, and can also be used for dyeing wool and nylon fibers. The dyes dye the fibers through their own affinity, and then they are firmly bonded to the fibers through covalent bonds under the action of alkali agents. |
| Insoluble azo dyes | During the dyeing process, the diazo component (chromophore) and the coupling component (chromophore) react directly on the fiber to form an insoluble color lake, which is called an insoluble azo dye. | This type of dye is mainly used for dyeing and printing cellulose fibers. The color base is first diazotized, and then dyed to the fiber fabric primed with chromophore through affinity, and then coupled to form an insoluble color lake and firmly exist on the fabric. |
| Disperse dyes | Disperse dyes are a type of nonionic dyes with simple structure, extremely low water solubility, and mainly exist in the form of dispersed tiny particles in the dye bath. The chemical structure of disperse dyes is mainly azo and anthraquinone, and there are also heterocyclic disperse dyes. | Disperse dyes are mainly used for dyeing and printing polyester fibers, and can also be used for dyeing acetate fibers and polyamide fibers. When dyeing, the dye must be evenly dispersed in the dye solution with the help of a dispersant, and then various synthetic fibers are dyed. |
| Reduction dyes | Reduction dyes are mostly polycyclic aromatic compounds, and their molecular structure does not contain water-soluble groups such as sulfonic acid groups and carboxylic acid groups. Their basic feature is that they contain two or more carbonyl groups in the conjugated double bond system of the molecule, so the carbonyl groups can be reduced to hydroxyl groups under the action of insurance powder, and become soluble leuco sodium salts in alkaline aqueous solution. | Reduction dyes are mainly used for dyeing cellulose fibers. When dyeing, they are reduced to water-soluble leuco sodium salts in an alkaline solution containing a reducing agent (such as Na2S2O4, sodium dithionite, commonly known as insurance powder) and then dyed with fibers, and then oxidized to become insoluble dyes and fixed on the fibers. |
| Sulfur dyes | Sulfur dyes are a type of water-insoluble dyes, generally made by mixing aromatic amines or phenolic compounds with sulfur or sodium polysulfide and heating them. This process is called sulfurization. | Sulfur dyes are mainly used for dyeing cellulose fibers. During dyeing, they are reduced to a soluble state in an alkaline sulfide solution. After dyeing the fibers, they are oxidized and fixed to the fibers in an insoluble state. |
| Condensation dyes | Condensation dyes are a type of dye that can form covalent bonds between the dye molecules themselves or with compounds other than the fiber during or after dyeing, thereby increasing the molecular size. Condensation dye molecules contain thiosulfate groups (-SSO3Na). Under the action of sodium sulfide, sodium polysulfide, etc., they can remove sulfite from the thiosulfate groups and form -S-S- bonds between dye molecules, so that two or more dye molecules are combined into an insoluble state and fixed on the fiber. | Condensation dyes are soluble in water. They can remove water-soluble groups on the fiber and undergo intermolecular condensation reactions, becoming insoluble dyes with a relatively large molecular weight and fixed on the fiber. At present, this type of dye is mainly used for dyeing and printing cellulose fibers, and can also be used for dyeing vinylon. |
| Fluorescent whitening agents | Fluorescent whitening agents can be regarded as a type of colorless dyes. After being dyed onto substrates such as fibers and paper, they can absorb ultraviolet rays and emit blue light, thereby offsetting the yellowness caused by excessive yellow light reflection on the fabric, and visually producing a white and dazzling effect | Different types of fluorescent whitening agents can be used for whitening treatment of various fibers. They are directly treated on the fabric and fixed on the fiber through their own affinity or cross-linking agents. |
