Classification of Dyes

Dye are colored organic compounds that can dye fibers or other substrates to a certain color. Dye must meet the following two requirements: First, It should soluble in water, or can be converted into a soluble state during dyeing and have a certain affinity for fibers. Second, the fiber can be colored by dyes and has a certain color fastness after dyeing. According to the application of dye, it can be divided into the following categories:

1 Acid dyes

These dye molecules contain sulfonic acid groups or carboxyl groups, which usually exist in the form of water-soluble sodium salts. They can stain protein fibers and nylon in acidic or weakly acidic media, but they cannot stain cellulose fibers. Acid mordant dyes also can be included in this category. Acid mordant dyes are similar to acid dyes and ortho-position of their azo group has hydroxyl groups or carboxyl groups, which can be bonded to the metal. After being treated with a metal mordant, the dye can form a strong complex with the metal.

1 Acid complex dyes and neutral dyes

Acid complex dyes are complexes formed with certain metal ions during dye production. Among them, the molecular structure contains only one or two sulfonic acid groups. Azo dyes and metal ions twisted together in a ratio of 1:1. This dye is soluble in water and primarily dyes woolen fabrics in a strong acid bath. If a two-molecule monoazo dye react with a metal ion to form a 2:1 type of metal complex dye, namely, neutral dye. Its water-solubility is worse than that of acid complex dyes. It can be used to dye wool, vinylon, nylon in weak acid or neutral dye baths.

3 Direct dye

Most direct dyes are azo dyes containing sulfonic acid groups and are soluble in water. Due to the unique structure of the dye itself, it has a strong affinity for cellulose fibers, and can directly dye cotton and viscose fabrics in a weakly alkaline or neutral dye bath, but such dyes have poor washing fastness.

4. Insoluble azo dye

Insoluble azo dye is also known as ice dyes or naphtol dyes. It consists of a diazo agent and a coupler. Bottoming with a coupling agent and then diazotizing the diazo agent to form a dye on the fabric. Since the dye is insoluble in water, it is called insoluble azo dye and is mainly used for the dyeing of cotton fabrics.

5. Sulfur dye

Sulfur dye is insoluble in water. It need to be reduced to soluble leucosome by sodium sulfide when dyeing. After oxidation, It becomes insoluble dye and fix on the fibers. It is mainly used for the dyeing of cotton fabrics.

6 Reducing dye

It also known as indanthrene dye. It is insoluble in water itself, and it needs to be reduced to the leuco-sodium salt in the alkaline medium when dyeing, and then absorbed by the fiber, and then oxidized by air or oxidant to become the original dye. This dye is mainly used for the dyeing of cotton and vinylon.

7 Reactive dye

Reactive dyes contain reactive groups in their molecular structure. When dyeing, they can form covalent bonds with hydroxyl groups or amino groups in the fiber molecules, that’s why they are called reactive dyes. Reactive dyes are mainly used for the dyeing of cotton, linen, silk, they can also be used for the dyeing of wool and synthetic fibers.

8. Disperse dye

The dye molecules do not contain water-soluble groups, and has poor solubility in water. When dyeing, the dyes are dispersed into ultra fine particles by dispersantand and then dyed by the fine particles. It is mainly used for the dyeing of synthetic fibres, such as the dyeing of polyesters, acetate fibres, and nylon fibers.

9 Cationic dye

In solution, cationic colored groups and anions can be ionized. It mainly used for dyeing of acrylic fibers.

10 Organic pigment

It used in the dyeing of inks, paints, etc.

11 Fluorescent brightener

This is a colorless dye that absorbs UV light when it is dyed into a fiber matrix.

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