What is cotton dyeing?

1. 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.

2. Printing dyes mainly include reactive dyes, insoluble ammonia dyes, stable insoluble ammonia dyes, vat dyes, soluble vat dyes and printing coatings.

3. Viscose fiber, which is similar to cotton fiber, 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. .

IV. The following is a brief introduction to the dyeing and printing properties of commonly used dyes for pure cotton fabrics.

1 Direct dyes 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 increase the amount of impurities on the dye. Direct dyes have a complete chromatogram, the dyeing method is simple, and the price is relatively cheap. They were once the main beam material of cotton fabrics. However, this dye is not good enough for dyeing, and needs to be fixed in post-processing.

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 to greatly improve the color fastness of dyed objects to washing and soaping. At the same time, it also has the advantages of easy dyeing and printing, bright colors, uniform color spectrum, and cheaper prices. However, generally reactive dyes have a low fixation rate and 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. For printing, one-phase or two-phase printing should be selected according to different dye types. There are also some reactive dyes that have poor color fastness to chlorine bleaching and weather resistance.

3 Vat dyes Vat dyes are insoluble in water and cannot be dyed directly. It needs to be reduced to a leuco body in an alkaline strong reducing solution of caustic soda and insurance powder. The leuco body dyes the cotton fiber. After oxidation, it returns to an insoluble dye and is fixed on the fiber. Vat dyes have a complete chromatogram, bright colors, and excellent color fastness to sunlight and soaping. However, due to their high price, some yellow and orange varieties are photosensitive and brittle, so their application is subject to certain restrictions. When dyeing or printing, it is necessary to strengthen the post-soap treatment to remove floating colors and improve the brightness.

4 Soluble vat dyes 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 dye and return it to insoluble form. The vat dye is dyed on the fiber. The dyeing process of soluble vat dyes is relatively simple, the dyeing is relatively uniform, and the dyeing fastness is high. However, this dye is expensive and is mainly used for dyeing and printing of light and medium-colored cotton fabrics.

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 sunlight resistance, 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 upper dyes, a middle primer (color phenol) and a color developer (color base). When dyeing, the fabric is first primed with a caustic soda solution of naphthol, and then developed with a diazotized solution of the color base. The naphthol on the fabric couples with the diazo compound of the color base to form an insoluble azo dye, which is fixed to the fabric. superior. Since ice is required for the diazotization reaction of the color base, insoluble azo dyes are also called ice dyes. This type of dye has bright color, good color fastness to soaping, and good color fastness to sunlight, but poor color fastness to rubbing and even worse color fastness to wet rubbing.

7 Stable and insoluble azo dyes Stable and 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. After certain treatment after printing, the temporarily stable diazo compounds are converted into active diazo compounds, and then couple with the phenol to form a non-dark azo dye. This type of dye is mainly used to print small patterns.

5. Classification of reactive dyes currently used on the market:

1. Medium-temperature reactive dyes 1, which have high fixation rate and easy washability, and are used for dip dyeing and Continuous dyeing.

2. Medium-temperature reactive dye 2, with high fixation rate and easy washability, used for dip dyeing and continuous dyeing.

3. Medium-temperature reactive dye 3, with high fixation rate, used for exhaust dyeing and continuous dyeing, especially suitable for blended dyeing of protein fibers and cellulose fibers.

4. High-temperature reactive dyes with high dye migration and leveling properties are used for exhaust dyeing, especially suitable for dyeing difficult-to-dye textiles.