What is the process of dyeing and printing performance of reactive dyes on dyes commonly used in pure cotton fabrics?
1. Direct dyes Direct dyes are soluble in water, and can be used to dye cotton fibers directly in neutral or weakly alkaline solutions. Adding neutral electrolytes such as table salt during dyeing can increase the amount of impurities on the dye. Direct dye chromatography is complete, the dyeing method is simple, and the price is relatively cheap. It used to be the main beam material of cotton fabrics. However, the dyeing of this dye is not good enough, and it needs to be fixed in the post-treatment.
2. Reactive dyes Reactive dyes refer to soluble dyes containing reactive groups. Under appropriate conditions, it can chemically combine with cellulose fibers and protein fibers, greatly improving the color fastness of the washed and soaped dyed objects. At the same time, it also has the advantages of dyeing, easy printing, bright color, uniform chromatography, and cheaper prices.
However, the fixing rate of general reactive dyes is not high, and it is easily hydrolyzed in alkaline solution, causing floating color. Therefore, when dyeing the fabric, the method of first dyeing and then fixing is used to improve the fixing rate of the dye. For printing, one-phase or two-phase printing should be used according to different 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 leuco in caustic soda, strong alkaline alkaline reducing solution, dyed cotton fiber from leuco, after oxidation, it will be restored to insoluble dye and fixed on the fiber.
The vat dyes have complete chromatograms, bright colors, and good color fastness to sunlight and soaping. However, due to the relatively high price, certain yellow and orange varieties have photosensitivity and brittle damage, so their application is restricted. When dyeing or printing, it is necessary to strengthen the post-treatment of soap boiling to remove floating colors and improve the vividness.
4. Soluble vat dyes Soluble vat dyes are derivatives of vat dyes. They are soluble in water. After dyeing on fibers, they need to be oxidized in acid solution to hydrolyze and oxidize the dyes and restore them to insoluble vat dyes. On the fiber. The dyeing process of soluble vat dyes is relatively simple, the dyeing is relatively transparent, and the dyeing fastness is high. But this kind of dye is expensive, mainly used for dyeing and printing of light and medium color cotton fabrics.
5. Sulfur dyes Sulfur dyes are insoluble in water, but can be dissolved in sodium sulfide solution and reduced to leuco. After the leuco is absorbed by cotton fiber, it is oxidized into insoluble dye and fixed on cotton fiber. Sulfur dyes are mainly used for dyeing cotton fiber dark products. Washing and sun exposure are good. The dyeing method is simple and cheap, but the color fastness to rubbing is poor, and the color is not bright enough.
Some dyes (such as sulfide black), during fabric storage, will make the fiber brittle, so anti-brittle treatment is required after dyeing. Yellow and orange sulfur dyes often have a photosensitive brittle effect on fibers.
6. Insoluble azo dyes Insoluble azo dyes are composed of two base dyes (chromophenol) and developer (chromophore). When dyeing, the fabric is first made with a caustic soda solution of naphthol, and then developed with a diazonium solution of the chromophore. The chromophenol on the fabric and the diazo compound of the chromophore are coupled to melon to form an insoluble azo dye, which is fixed on the fabric on.
Since the chromophore needs to use ice during the diazotization reaction, the insoluble azo dye is also called ice dye. This kind of dye has bright color, good color fastness to soaping, and good color fastness to sunlight, but the color fastness to rubbing is poor, and the color fastness to wet rubbing is even worse.
7. Stable insoluble azo dyes Stable insoluble azo dyes are mixtures of naphthol sodium salt and temporarily stable diazo compounds. Under normal circumstances, the two do not undergo a coupling reaction. After a certain treatment after printing, the temporarily stable diazo compound is converted into a live diazo compound, which is coupled with naphthol to form a non-deep azo dye. This type of dye is mainly used for printing small patterns.