What are the types of dyes

1. Direct dyes

Structural properties: Direct dyes are a kind of water-soluble anionic dyes. Most of the dye molecules contain sulfonic acid groups, and some have carboxyl groups. The dye molecules and cellulose molecules are combined by van der Waals forces and hydrogen bonds. 

Dyeing objects and methods: Direct dyes are mainly used for dyeing cellulose fibers, but also for dyeing silk, paper, and leather. During dyeing, the dye is directly dyed on the fiber in the dye liquor, and is adsorbed on the fiber through van der Waals force and hydrogen bond.

2. Acid dyes

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

Dyeing objects and methods: commonly used for dyeing silk, wool and polyamide fibers and leather. Acid dyes dye fibers through their own affinity and bond with fibers by ionic bonds; acid mordant dyes have similar dyeing conditions to acid dyes, but they need to be chelated on the fiber through the action of certain metal salts to obtain good results. Washing resistance; acid mordant dyes, some acid dyes have chelated metal ions in their molecules, have low hydrolysis tendency and good dye fastness.

3. Cationic dyes

Structural properties: Cationic dyes are soluble in water and are in a cationic state. Early dye molecules have basic groups such as amino groups, often in the form of acid salts.

Dyeing objects and methods: Mainly used for dyeing polyacrylonitrile fibers, which can be combined with carboxyl anions in protein fiber molecules such as silk in the form of salt bonds during dyeing.

4. Reactive dyes

Structural properties: reactive dyes are also called reactive dyes. The molecular structure of this type of dye contains active groups, which can covalently bond with the hydroxyl and amino groups in the fiber molecule during dyeing to firmly dye the fiber.

Dyeing objects and methods: Reactive dyes are mainly used for dyeing and printing of cellulose fiber textiles, as well as for dyeing wool and nylon fibers. The dye dyes the fiber through its own affinity, and then firmly binds to the fiber through a covalent bond under the action of the alkali agent.

5. Disperse dyes

Structure and properties: Disperse dyes are non-ionic dyes with simple structure and extremely low water solubility. They mainly exist as dispersions of tiny particles in the dye bath. The chemical structure of disperse dyes is mainly based on azo and anthraquinones, as well as heterocyclic disperse dyes.

Dyeing objects and methods: Disperse dyes are mainly used for dyeing and printing of polyester fibers, but also for dyeing acetate fibers and polyamide fibers. When dyeing, the dye must be evenly dispersed in the dye liquor with the help of a dispersant, and then various synthetic fibers are dyed.

6. Vat dyes 

Structural characteristics: Vat dyes are mostly polycyclic aromatic compounds, and their molecular structure does not contain sulfonic acid groups, carboxylic acid groups and other water-soluble groups. 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 a hydroxyl group under the action of sodium hydroxide, and become a soluble hidden in the alkaline aqueous solution. Sodium salt of chromosome.

Dyeing objects and methods: Vat dyes are mainly used for dyeing cellulose fibers. During dyeing, they are reduced to water-soluble leuco sodium salt in an alkaline solution containing a reducing agent (such as Na2S2O4, sodium dithionite, commonly known as sodium sulfite) to dye the fiber, and then become insoluble dyes again after being oxidized. Fix to the fiber.

7. Sulfur dyes

Structural properties: Sulfur dyes are a type of water-insoluble dyes, which are generally prepared by mixing aromatic amines or phenolic compounds with sulfur or sodium polysulfide by heating. This process is called vulcanization.

Dyeing objects and methods: sulfur dyes are mainly used for dyeing cellulose fibers. During dyeing, they are reduced to a soluble state in the alkali sulfide solution. After dyeing the fiber, it becomes insoluble and fixed on the fiber after oxidation.

8. Fluorescent brightener

Structural properties: fluorescent brighteners can be regarded as a kind of colorless dyes. After they are dyed on fiber, paper and other substrates, they can absorb ultraviolet rays and emit blue light, thereby offsetting the excessive yellow light reflection on the fabric. The yellow feeling produces a white and dazzling effect visually 

Dyeing objects and methods: different types of fluorescent whitening agents can be used for whitening treatment of various fibers. They are directly processed on the fabric and fixed on the fiber by their own affinity or cross-linking agent.