The dyes used for dyeing pure cotton fabrics mainly include direct dyes, reactive dyes, vat dyes, soluble vat dyes, insoluble ammonia dyes, sulfur dyes, etc. Printing dyes mainly include reactive dyes, insoluble ammonia dyes, stable insoluble ammonia dyes, vat dyes, soluble vat dyes and printing coatings. Viscose fibers similar to cotton fibers can also be dyed and printed with the various dyes mentioned above. However, since viscose fiber is a regenerated cellulose fiber with a looser structure, compared with cotton fiber, it is less resistant to alkali and more sensitive to acid. Therefore, when dyeing with this type of dye, the process and other aspects should be different. . The following is a brief introduction to the dyeing and printing properties of commonly used dyes for pure cotton fabrics.
【1】Direct dye Direct dyes can be dissolved in water and can be directly dyed on cotton fibers in neutral or weakly alkaline solutions. Adding neutral electrolytes such as salt during dyeing can directly increase the amount of impurities on the dye. The dye has a complete chromatogram, the dyeing method is simple, and the price is relatively cheap. It was once the main material of cotton fabrics. However, the dyeing fastness of this dye is not good enough, and it needs to be fixed in the post-processing.
【2】Reactive dyes Reactive dyes refer to soluble dyes containing reactive groups that can chemically combine with cellulose fibers and protein fibers under appropriate conditions to greatly improve the color fastness of the dyed object to washing and soaping. etc. At the same time, it also has the advantages of easy dyeing and printing, bright colors, relatively uniform color spectrum, and cheaper prices. Generally, the fixation rate of reactive dyes is not high, and they are easily hydrolyzed in alkaline solutions, causing floating colors. Therefore, when dyeing fabrics, the method of dyeing first and then fixing is used to improve the fixation rate of the dye. The dye should be used for printing. Depending on the variety, one-phase or two-phase printing is used. Some reactive dyes have poor color fastness to chlorine bleaching and weather resistance.
【3】Vat dye Vat dyes are insoluble in water and cannot be dyed directly. They need to be reduced to leuco bodies in an alkaline strong reducing solution of caustic soda and insurance powder. Cotton fibers are dyed from the leuco bodies and then oxidized. , restored to insoluble dye and fixed to the fiber. It has a complete color spectrum, bright color, and excellent color fastness to sunlight and soaping. However, due to its high price, some yellow and orange varieties have photosensitive brittleness, so their application is subject to certain restrictions in dyeing or printing. It is necessary to strengthen the post-soap treatment to remove floating colors and improve the brightness.
【4】Soluble vat dye Soluble vat dyes are derivatives of vat dyes and are soluble in water. After dyeing on fibers, they need to be oxidized in an acid solution to hydrolyze and oxidize the dyes and restore them to insoluble vat dyes. The dyeing process of soluble vat dyes is relatively simple, and the dyeing is relatively transparent and has high dye fastness. However, this dye is expensive and is mainly used for dyeing and printing of light and medium-colored cotton fabrics. p>
【5】 Sulfur dyes Sulfur dyes are insoluble in water, but can be dissolved in sodium sulfide solution and reduced to leuco bodies. After the leuco bodies are absorbed by cotton fibers, they are oxidized into insoluble dyes and fixed on the cotton fibers. Sulfur dyes are mainly used for dyeing dark-colored cotton fiber products. They have good washing and sun exposure properties, simple dyeing methods, and cheap prices. However, their color fastness to rubbing is poor and their colors are not bright enough. Certain dyes (such as sulfur black) will cause the fibers to become brittle during storage, so anti-brittle treatment is required after dyeing. Yellow and orange sulfur dyes often cause photosensitive brittleness to fibers.
【6】Insoluble azo dyes Insoluble azo dyes are composed of two dye intermediate primers (chromophen) and color developers (color base). When dyeing, the fabric is first primed with a caustic soda solution of naphthol, and then. The color is developed using a diazotized solution of the color base. The phenol on the fabric is coupled with the diazo compound of the color base. It becomes an insoluble azo dye and is fixed on the fabric. Since ice is required for the diazotization reaction of the color base, this type of dye is also called ice dye and has bright color and good color fastness to soaping. The color fastness to sunlight is also good, 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 a mixture of naphthol sodium salt and temporarily stable diazo compounds. Under normal circumstances, the two do not undergo a coupling reaction and become temporarily stable after certain treatment after printing. Diazo compounds are converted into active diazo compounds, which are coupled with phenol to form non-dark azo dyes. These dyes are mainly used for printing small objects.block pattern.
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