What are reactive dyes and their advantages and disadvantages?

Reactive dyes are a new type of water-soluble dyes that appeared in the 1950s. Reactive dye molecules contain reactive groups that can react with hydroxyl groups in cellulose and amino groups in protein fibers, and form covalent bonds with fibers during dyeing. , The formation of "dye-fiber" compound. Reactive dyes have the characteristics of bright colors, good level dyeing, simple dyeing method, high dye fastness, complete chromatogram and low cost. They are mainly used in cotton, linen, viscose, silk, wool and other fibers and their blended fabrics. Dyeing and printing.

1. Craft

The dyeing method of reactive dyes; reactive dyes dye cotton, the most commonly used dyeing method: dip dyeing, in addition to pad dyes. Dip dyeing method: The dip dyeing method can be divided into one-bath one-step method, one-bath two-step method, and two-bath method. A: One-bath and one-step method: Dyeing is performed in an alkaline bath, that is, the color is fixed while dyeing. This method has simple process, short dyeing time and convenient operation, but because the adsorption and fixing are performed at the same time, after fixing The dye can no longer diffuse, so the level dyeing and translucent dyeing are poor. When dyeing in the same alkaline condition, the dye stability of the dye bath is more hydrolyzed. B: One-bath two-step method: First dye in a neutral bath. When the dye uptake is close to equilibrium, add an alkali agent to the dye bath to adjust the PH value to the fixed PH value (usually 11). Covalently bond with fiber to achieve color fixation. The one-bath two-step method is a more reasonable dyeing method in the reactive dye dip dyeing method. It can not only obtain a higher dye uptake and fixation rate. And it has a good leveling effect, so this method is commonly used for dyeing cotton knitted fabrics.

2. Advantages

Reactive dyes are composed of parent dyes, linking groups and active groups, which enable them to form strong covalent bonds with fibers during use, and have a series of unmatched characteristics of other cellulose fiber dyes, establishing their role The key status of the development and use of dyes for cellulose fibers is prominently embodied in the following four aspects:

(1) Reactive dyes are one of the best choices to replace prohibited dyes and other types of cellulose dyes such as sulfur dyes, ice dyes and vat dyes.

(2) Reactive dyes can use economical dyeing technology and simple dyeing operations to obtain high levels of various fastness properties, especially wet fastness.

(3) Reactive dyes have wide chromatograms, bright colors, excellent performance and strong applicability, and their hue and performance are basically in line with the market's requirements for fibers and clothing.

(4) Reactive dyes are suitable for printing and dyeing of new cellulosic fiber products such as Lyocell fiber.

3. Disadvantages

However, the main technical problems of reactive dyes are as follows:

(1) The utilization rate is not high enough, generally 60%~70%, which produces a large amount of colored sewage, the chroma of which exceeds several thousand times, the COD value is generally 8,000 to 30,000 ppm, and the COD value of concentrated wastewater exceeds 50,000 ppm. 

(2) In order to suppress the charge on the fiber surface, the reactive dyes need to consume a considerable amount of electrolyte when used, which not only increases labor intensity, but also causes the chloride ion concentration in the wastewater to reach more than 100,000 ppm, which greatly increases the treatment reactivity The difficulty of dyeing wastewater.

(3) Certain color fastnesses cannot meet market requirements, such as light fastness to perspiration, wet rubbing fastness, and light fastness of azo red dyes and azo blue dyes in light colors.

(4) There are fewer dark varieties that can replace vulcanizates and vat dyes.

4. Functional use

Reactive dyes are composed of parent dyes, linking groups and active groups, which enable them to form strong covalent bonds with fibers during use, and have a series of unmatched characteristics of other cellulose fiber dyes, establishing their role The key status of the development and use of dyes for cellulose fibers is prominently represented in the following four aspects:

(1) Reactive dyes are one of the best choices to replace prohibited dyes and other types of cellulose dyes such as sulfur dyes, ice dyes and vat dyes.

(2) Reactive dyes can use economical dyeing technology and simple dyeing operations to obtain high levels of various fastness properties, especially wet fastness.

(3) Reactive dyes have wide chromatograms, bright colors, excellent performance and strong applicability, and their hue and performance are basically in line with the market's requirements for fibers and clothing.

(4) Reactive dyes are suitable for printing and dyeing of new cellulosic fiber products such as Lyocell fiber.