The dyes used for dyeing cotton fabrics mainly include direct dyes, reactive dyes, vat dyes, soluble vat dyes, insoluble azo dyes, sulfur dyes, etc. Printing dyes mainly include reactive dyes, insoluble azo dyes, stable insoluble azo dyes, vat dyes, soluble vat dyes, and printing coatings. Viscose fibers similar to cotton fibers can also be dyed and printed with the above-mentioned various dyes. However, because the viscose fiber is a regenerated cellulose fiber, the structure is looser. Compared with cotton fiber, it is not alkali resistant and more sensitive to acid. Therefore, when dyeing with this kind of dyes, there should be differences in process and other aspects. . The following briefly introduces the dyeing and printing properties of commonly used dyes for pure cotton fabrics.
1. Direct dye
Direct dyes are soluble in water and can directly dye cotton fibers in neutral or weak alkaline solutions. Adding neutral electrolytes such as salt during dyeing can increase the amount of impurities on the dye. The direct dye chromatogram is complete, the dyeing method is simple, and the price is relatively cheap. It was once the main beam material for cotton fabrics. However, this dye-dyed cell is not good enough, and it needs to be fixed in post-treatment.
2. Reactive dyes
Reactive dyes refer to soluble dyes containing reactive groups. Under proper conditions, it can chemically combine with cellulose fibers and protein fibers, greatly improving the colorfastness to washing and soaping of the dyed material. At the same time, it also has the advantages of easy dyeing, simple printing, bright color, better color spectrum, and lower price. However, the fixing rate of general reactive dyes is not high, and it is easy to hydrolyze in alkaline solution, causing floating color. Therefore, the method of dyeing first and then fixing is used to improve the fixing rate of dyes. For printing, one-phase or two-phase printing should be selected according to the different types of dyes. Some reactive dyes have poor color fastness to chlorine bleaching and weathering.
3. Vat dyes
Vat dyes are insoluble in water and cannot be dyed directly. It needs to be reduced to a leuco body in a strong alkaline reducing the solution of caustic soda and sodium hydroxide. The cotton fiber is dyed from the leuco body, and after oxidation, it returns to an insoluble dye to be fixed on the fiber. The chromatogram of vat dyes is complete, the color is bright, and the colorfastness to sunlight and soaping is good. However, due to the relatively high price, some yellow and orange varieties have photosensitivity and fragility, so their application is limited. When dyeing or printing, the post-soaping treatment should be strengthened to remove the floating color and improve the vividness.
The above information is provided by the muslin fabric factory.