Analysis of reactive dyes and direct dyes

Reactive Dyes refers to a class of water-soluble dyes with reactive groups in the dye molecule. The molecular structure is usually composed of two parts: the dye precursor and the reactive group. The dye precursor reacts with the fibers through the reactive group during dyeing. The covalent bond gives a stable "dye-fiber" colored compound as a whole, which makes the dyed product have good washing fastness and rubbing fastness. The reactive dye has bright color. The chromatogram is complete. The price is lower. The dyeing process is simple. Good dyeing properties, mainly used for dyeing cotton fibers and their textiles. Printing. Can also be used for the dyeing of hemp, wool, silk and some synthetic fibers. It is an important dye in the dye industry.
If the reactive dyes are classified according to the structure of the dye precursor, there are azo type, 蒽醌 type, 酞箐 type, etc. However, usually the reactive dyes are classified according to the structure of their active groups, such as the tricus trihalide Benzene type (or homotriazine type) reactive dyes; vinyl sulfone type reactive dyes with vinyl sulfone groups, etc. With the development of production technology, the types of reactive groups are increasing, and the variety of reactive dyes is increasing. .
The dyeing mechanism of reactive dyes involves two processes: color absorption and fixation. The color absorption is both the dye and water molecules entering the fiber and being absorbed by the fiber. Therefore, the reactive dye molecules contain hydrophilic groups and have good water solubility. The fixation is a reaction between a reactive group in a dye molecule and a group in a fiber molecule to form a new covalent bond.
Due to the excellent performance of reactive dyes, the application range is expanding, and new products are constantly emerging. In today's development trend, the concentrated performance is: development of high fixation rate. High color fastness. Suitable for low salt, low water, low energy dyeing requirements. New dye varieties to meet the requirements of environmental protection, the development of new varieties in the dye matrix is ​​the development of high direct reactive dye color bodies, mainly azo-type hair color bodies. And more is the development of new active groups And the new active groups that have been put into production are: monofluoro-s-triazine, nicotinic acid, s-triazine, trichloropyrimidine, difluoro-chloropyrimidine, dichloroquinoline, a-bromoacrylamide, etc. The introduction of dyes has greatly improved in terms of vividness, fastness and fixing rate. Dyes containing complex reactive groups have been developed due to their excellent application performance and low price.
Currently in production: KE type with two monochlorotriazine groups; M type with one monochlorotriazinyl group and one vinylsulfone group, one of which has a chlorotriazine and a meta-ester Combined type ME (or type B); chloroform with monochlorotriazine and para-ester, and new varieties with three active groups. The production of these new varieties accelerates the greening process of reactive dyes. From the development trend, reactive dyes are gradually replacing the reduction. Direct. Vulcanization. Ice dyes have become the main varieties in cellulose fiber dyes, and are being applied to dyeing with protein fibers and synthetic fibers.
X type ------ dichloro-triazine type
K type ------ monochloro-triazine type
KN type----vinyl sulfone type
M type ------ monochlorotriazine. vinyl sulfone double active type
Type KE-----Direct DYES is a type of dye that can directly dye cellulose fibers in neutral or weakly alkaline media. It usually does not need to be dyed with mordant. In the bath, you only need to add salt or Yuanming powder to boil, you can dye it. He usually combines the hydrogen bond between cellulose and dye and van der Waals force, so it is washable. The light fastness is poor. The light fastness is in Grade 5 or higher is called direct lightfast dye.
The direct dye has a complete chromatogram from yellow to black, the production process is simple, the price is low, and the use is convenient. Therefore, it is widely used in knitting, silk, cotton spinning, ribbon, leather, wool, paper, etc. It is also used in viscose fiber. Dyeing.
Direct dye molecules are generally larger than other dye molecules, and are mainly composed of azo and polyazo structures derived from various diamine compounds. The first use of biphenyl diamines and stilbene is due to biphenyl. The carcinogenic effects of amine compounds have been banned in countries all over the world. Some new structures of dyes have been developed and applied, such as urea type, benzoylanilide type, melamine type, benzimidazole type, thiazole type, diazine. Type. Copper bismuth type and polyazo type. In order to improve the light fastness and wash fastness of direct dyes, copper complex type direct dyes have also been developed and used, and fixing agents are used in the dyeing process. A fixing agent is available.
In particular, melamine-type direct dyes should be proposed. Due to the introduction of a triazine ring group, their fastness to washing and washing are better than that of benzidine-type direct dyes, and these dyes have high temperature stability and dyeing. The rate is high, the pH value of the dyeing bath is wide, suitable for dyeing with the disperse dye in the same bath, and the polyester has less staining. Therefore, it has been paid attention to by various countries and has formed a separate series, collectively referred to as D-type direct blending dye.
Another new discovery of direct dyes is the appearance of reactive direct dyes (or direct cross-linking dyes). This is a class of copper-complexed polyazo direct dyes that are used in conjunction with specific fixing agents for dyeing. Most of these fixing agents are cationic macromolecular compounds, which can produce covalent bonds, ionic bonds or coordination bonds with dyes and cellulose molecules, respectively, while fixing the color, thereby greatly improving dye dyeing. Degree and fixing rate, suitable for one-bath one-step dyeing of polyester/cotton fabrics. The disadvantages are all copper complexes, which make the dyed fabrics darker.

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