Vat Blue Dyes
VAT dye refers to the reduction under alkaline conditions to color the fiber, and then by oxidation, on the fiber to restore the original insoluble stainer, used for dyeing cellulose fiber; The insoluble VAT stainer is made into sulfate sodium salt and changed into soluble VAT stainer, which is mainly used in cotton printing.
It is insoluble in water, dyeing to reduce solution in the alkaline strong reducing solution to leucotroph sodium salt can be infected with fiber, after oxidation, restore insoluble stainer lake and fixed on the fiber, generally washable, fastness to the sun is higher. Such as shilin blue and so on. The main cotton and polyester-cotton blended fabric dyeing; Nylon can also be colored; In the silk industry, it is used for rayon, rayon and rayon interweaving, and discharge printing of real silk.
Vat dyes, also known as urn dyes, are insoluble in water and cannot be used directly to dye fabrics. When it is used for dyeing, it needs to be reduced to a water-soluble Cryptochrome in an alkaline solution with sodium sulfite, which can be absorbed by the fiber, and then it can be oxidized and colored by air and so on, so that the cryptochrome can be converted into the original dye and dyed in the fiber. According to the structure, the dyes can be divided into anthraquinone group and indigo group. The former is reduced blue RSN, reduced Brown BR, reduced grey, etc.; the latter is reduced blue 2B, reduced peach red, etc. Reducing dyes usually have complex molecular structure. However, they are often composed of some simple basic structures. Anthraquinone is the basic structure of anthraquinone group, and indigo and thioindigo are the basic structures of indigo group. Moreover, they all contain carbonyl C = o. This group has the property of hydrogenation and reduction, and the reaction in the dyeing process is carried out on this group. After the successful development of reactive dyes, although some of them are replaced by this kind of dyes, they are still very important dyes for the dyeing of cellulose fiber textiles. Vat dyes can also be used for vinylon dyeing. Some reducing dyes can be used as disperse dyes to dye polyester fibers. The main disadvantage of reducing dyes is that the red color is not as rich as azo dyes, and it is generally more expensive, and the price of new reducing agents is also higher. In particular, some yellow, orange and red vat dyes will cause brittle damage of silk and fiber in the sun, which should be paid attention to in selection.
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