Classification of dyes

I. Classification of dyes according to their chemical structure or their characteristic groups is called chemical classification

They are divided into: azo dyes, anthraquinone dyes, arylmethane dyes, indigo dyes, sulphur dyes, phthalocyanine dyes, nitro and nitroso dyes, in addition to other structural types of dyestuffs, such as methanoguan and multimethanoguan dyestuffs, stilbene dyestuffs, and a wide range of heterocyclic dyestuffs.

Second, according to the performance of dyes and application methods for classification, known as the application of classification

Divided into: direct dyes, acid dyes, cationic dyes, reactive dyes, insoluble azo dyes, disperse dyes, reducing dyes, sulfide dyes, condensation dyes, fluorescent whiteners, in addition to oxidation dyes used for textiles (e.g., aniline black), solvent dyes, polypropylene dyes, as well as food coloring used for food, and so on.

Name of Dyes

Structural Properties and Characteristics

Dyeing Objects and Methods

Direct dyes

Direct dyes are a class of water-soluble anionic dyes. Most of the dye molecules contain sulfonic acid group, some have carboxylic acid group, and the dye molecules and cellulose molecules are combined with van der Waals force and hydrogen bonding.

Direct dyes are mainly used for dyeing cellulose fibers, but can also be used for dyeing silk, paper and leather. When dyeing, the dyes are directly applied to the fibers in the dye solution and adsorbed on the fibers through van der Waals force and hydrogen bonding.

Acid dyes

Acid dyes are a class of water-soluble anionic dyes. The dye molecule contains sulfonic acid group, carboxyl group and other acidic groups, usually in the form of sodium salt, in the acidic dye bath can be combined with the amino group in the protein fiber molecule by ionic bond, so it is called acid dyes.

Commonly used in silk, wool and polyamide fibers and leather dyeing. Acid dyes, through its own affinity on the dyeing fiber, and ionic bonding and fiber binding; acid mordant dyes, its dyeing conditions and acid dyes are similar, but need to be through the role of certain metal salts, the formation of chelates in the fiber in order to obtain a good washing performance; acid-containing mordant dyes, there are a number of acid dyes with chelating metal ions in the molecule, the tendency of hydrolysis is small, dyeing fastness is good.

Cationic dyes

Cationic dyes are soluble in water and present cationic state. Early dye molecules have alkaline groups such as amino group and often exist in the form of acid salt.

Mainly used in the dyeing of polyacrylonitrile fibers, when dyeing can be combined with the carboxyl negative ions in the protein fiber molecules such as silk in the form of salt bonds.

Reactive dyes

Reactive dyes are also known as reactive dyes. These dyes contain reactive groups in their molecular structure, which can covalently combine with hydroxyl and amino groups in fiber molecules when dyeing and firmly dye on the fiber.

Reactive dyes are mainly used for dyeing and printing of cellulose fiber textiles, but can also be used for dyeing wool and nylon fibers. The dyestuffs dye the fibers by their own affinity, and then firmly bind to the fibers through covalent bonding under the action of alkaline agents.

Insoluble Azo Dyes

This type of dyestuff is dyed by reacting the diazo component (color base) and the coupling component (color phenol) directly on the fibers during the dyeing process, generating insoluble color precipitates and dyeing, which are called insoluble azo dyestuffs.

These dyes are mainly used for dyeing and printing of cellulose fibers. The chromophore is first diazotized and then dyed onto the fiber fabric primed with chromophenol by affinity, and then coupled to form an insoluble color precipitate that exists firmly on the fabric.

Disperse dyes

Disperse dyes are a class of non-ionic dyes with a simple structure, extremely low water solubility, and exist mainly as dispersions of tiny particles in the dye bath. The chemical structure of disperse dyes is dominated by azo and anthraquinone, and there are also heterocyclic disperse dyes.

Disperse dyes are mainly used in the dyeing and printing of polyester fibers, but can also be used in the dyeing of acetate fibers and polyamide fibers. When dyeing, the dyes must be evenly dispersed in the dye solution with the help of dispersants, and then dye all kinds of synthetic fibers.

Reducing dyes

Reducing dyes are mostly polycyclic aromatic compounds that do not contain water-soluble groups such as sulfonic acid and carboxylic acid groups in their molecular structure. Their basic feature is that they contain two or more carbonyl groups in the conjugated double bond system of the molecule, so they can reduce the carbonyl group to hydroxyl group under the action of the insurance powder and become soluble sodium salt of cryptochrome in alkaline aqueous solution.

Reducing dyes are mainly used for dyeing cellulose fibers. When dyeing, they are reduced to water-soluble sodium salt of cryptochrome in alkaline solution containing reducing agent (e.g., Na2S2O4, sodium dithionite, commonly known as insurance powder), and then oxidized to become insoluble dyes again and fixed on the fiber.

Sulfur dyes

Sulfur dyes are a class of water-insoluble dyes, generally made by mixing aromatic amines or phenolic compounds with sulfur or sodium polysulfide and heating, a process called vulcanization.

Sulfur dyes are mainly used for dyeing cellulose fibers. When dyeing, they are reduced to a soluble state in the sulfide alkali solution, and after dyeing the fibers, they are oxidized and become insoluble and fixed on the fibers.

Condensation dyes

Condensation dyes are a class of dyes in the dyeing process or after the dyeing process, the dyestuff itself between the molecules or with compounds other than fibers can occur covalent bonding, so as to increase the molecular dyestuff. Condensation dyes contain thiosulfate groups (-SSO3Na) in their molecules, which are formed in the presence of sodium sulfide, sodium polysulfide, and other substances.

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