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Brief introduction of dyes used in pure cotton fabric dyeing

The dyes used for pure cotton fabric dyeing mainly include direct dyes, reactive dyes, reducing dyes, soluble reducing dyes, insoluble even ammonia dyes, sulfurized dyes, etc. Printing dyes mainly include reactive dyes, insoluble azo dyes, stable insoluble azo dyes, reducing dyes, soluble reducing dyes and printing coatings. Viscose fibers of the same kind as cotton fibers can also be dyed and printed with the above dyes. However, viscose fiber is a kind of regenerated cellulose fiber, which has relatively loose structure. Compared with cotton fiber, viscose fiber is not alkali resistant and sensitive to acid. Therefore, when dyeing with this kind of dye, there should be some differences in process. The following is a brief introduction to the dyeing and printing properties of common dyes for pure cotton fabrics.

【1】 Direct dyestuff direct dyestuff can dissolve in water, in neutral or weak alkaline solution, can dye cotton fiber directly. The addition of neutral electrolytes such as salt can increase the amount of impurities on the dye. The direct dye chromatography is complete, the dyeing method is simple, and the price is cheaper. It used to be the main beam material of cotton fabric. However, the dyeing fastness of this dye is not good enough, so it needs to be fixed in the post-treatment.

【2】 Reactive dyestuffs reactive dyestuffs refer to soluble dyestuffs containing active groups. Under suitable conditions, it can combine with cellulose fiber and protein fiber, and improve the color fastness of the dyed substance in washing and soaping. At the same time, it also has the advantages of simple dyeing and printing, bright color, homogeneous chromatogram and cheaper price. However, the fixation rate of general reactive dyes is not high, which is easy to hydrolyze in alkaline solution, resulting in floating color. Therefore, the method of dyeing first and fixing later is used to improve the fixation rate of dyes. For printing, one-phase or two-phase printing method should be selected according to different dye varieties. Some reactive dyes have poor color fastness to chlorine bleaching and climate.

【3】 Vat dyes vat dyes are insoluble in water and cannot be dyed directly. It needs to be reduced to Cryptochrome in the alkaline strong reducing solution of caustic soda and sodium silicate powder. Cotton fibers are dyed from cryptochrome, oxidized, recovered to insoluble dyes and fixed to fibers. The color spectrum of vat dyes is complete and bright, while the color fastness of sun and soap washing is better. However, due to the high price, some yellow and orange varieties have the effect of photosensitive embrittlement, so they are limited in application. When dyeing or printing, it is necessary to strengthen the treatment after soaping to remove the floating color and improve the brightness.

【4】 Soluble vat dyestuff is a derivative of vat dyestuff, soluble in water. After dyeing on the fiber, it needs to be oxidized in the acid solution to make the dye hydrolyze, oxidize and return to insoluble vat dyestuff and dye on the fiber. The dyeing process of soluble vat dyes is simple, the dyeing is uniform, and the dyeing fastness is high. But the price of this dye is very high. It is mainly used for dyeing and printing of light and medium colored cotton fabrics.

【5】 Sulfurized dyestuffs sulfurized dyestuffs are insoluble in water, but can be dissolved in sulfurized sodium solution, reduced to cryptochrome, which is absorbed by cotton fiber, oxidized to insoluble dyestuffs and fixed on cotton fiber. Sulfurized dyes are mainly used in the dyeing of dark cotton fiber products. They are easy to dye and cheap, but they are not strong enough in rubbing and bright enough. Some dyes (such as black sulfide) will make the fiber brittle during the storage of the fabric, so anti brittle treatment is needed after dyeing. Yellow and orange sulfide dyes often have photosensitive embrittlement effect on fibers.

【6】 The insoluble azo dye is composed of two kinds of dyes (chromophenol) and chromogenic agent (chromophore). In dyeing, the fabric is first treated with caustic soda solution of chromophenol, and then colored with diazotization solution of chromobase. The chromophenol on the fabric and diazo compound of chromobase are coupled to form insoluble azo dye, which is fixed on the fabric. Because of the need of ice in diazotization reaction of color group, insoluble even ammonia dye is also called ice dye. This kind of dye has bright color, good color fastness to soaping and sunlight, but poor color fastness to rubbing and worse color fastness to wet rubbing.

【7】 Stable insoluble azo dye is a mixture of chromophenol sodium salt and temporarily stable diazo compound. In general, there is no coupling reaction between them. After a certain treatment after printing, the temporarily stable diazo compound is converted into active diazo compound, and then coupled with chromophenol to form azo dye with low depth. This kind of dye is mainly used for printing small patterns.