Reactive dyes, also known as 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. They react with fibers during dyeing. Covalent bonds are formed, creating "dye-fiber" compounds. Reactive dyes have the characteristics of bright colors, good dye leveling, simple dyeing methods, high dye fastness, complete chromatography and low cost. They are mainly used for dyeing cotton, linen, viscose, silk, wool and other fibers and their blended fabrics. and prints.
Definition
Reactive dyes are also called reactive dyes. The molecule contains chemically active groups that can react with cotton, wool and other fibers in aqueous solution to form co-bonded dyes. Has high wash fastness
Classification
According to different reactive groups, reactive dyes can be mainly divided into two categories.
Formula
Symmetrical triazine type, its general formula is:
In the formula, D is the parent dye. In this type of reactive dyes, the chemical properties of the active chlorine atom are more active. During dyeing, chlorine atoms are replaced by cellulose fibers in alkaline medium and become leaving groups. The reaction between dyes and cellulose fibers is a bimolecular nucleophilic substitution reaction (see substitution reaction).
Vinyl sulfone type: The active group contained in this type of reactive dye is vinyl sulfone group (D-SO2CH=CH2) or sulfate ester of β-hydroxyethyl sulfone group. During dyeing, β-hydroxyethyl sulfone sulfate undergoes an elimination reaction in an alkaline medium to generate a vinyl sulfone group, which is then combined with cellulose fibers and undergoes a nucleophilic addition reaction to form a covalent bond.
The above two types of reactive dyes are the main reactive dyes with the largest output in the world. In order to improve the fixation rate of reactive dyes, two reactive groups have been introduced into the dye molecules in recent years, which are called dual reactive dyes. In addition to varieties for cellulose fibers, reactive dyes have also been developed for protein fibers (such as silk, wool and other fibers).
Craftsmanship
Reactive dye dyeing methods; reactive dyes dye cotton, the most commonly used dyeing method: dip dyeing, and pad dyeing. Dip dyeing method: Dip dyeing method can be divided into three dyeing methods: one-bath one-step method, one-bath two-step method, and two-bath method.
A: One-bath one-step method: Dyeing is carried out in an alkaline bath, that is, fixation is performed while dyeing. This method has a simple process, short dyeing time, and easy operation. However, since adsorption and fixation are performed at the same time, after fixation The dye can no longer diffuse, so leveling and dyeing through are poor. When Tongjin dyes under alkaline conditions, the dyestuff in the dye bath is more stable and hydrolyzed.
B: One-bath two-step method: Dye first in a neutral bath. When the dye is close to equilibrium, add an alkali agent to the dye bath and adjust the pH value to the specified fixation pH value (usually 11). At this time, the dye Reach covalent bonding with fibers to achieve color fixation. The one-bath and two-step method is a more reasonable dyeing method among the reactive dye exhaust dyeing methods. It can not only obtain higher dye uptake rate and color fixation rate. It also has good level dyeing effect, so this method is commonly used for dyeing cotton knitted fabrics.