How much do you know about the dyeing process? What are the methods of dyeing fabrics?
Dyeing is a key process to produce color in fabrics or fiber yarns, and is a key process to enhance the value of textiles, such as adding patterns and patterns to textiles, changing the color of textiles and related pre-treatment processes.
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 methods of commonly used dyes for pure cotton fabrics.
dyeing process
The dyeing process can be roughly divided into three stages:
1. Absorbing
Adsorption is the process of dye attachment to the surface of the fiber; the dye is adsorbed by the fiber due to intermolecular forces, electrostatic attraction between ions, etc. in the solution.
2. diffusing and penetreating
After adsorption, the dye needs to enter the interior of the fiber and remain there; under certain conditions, the adsorbed dye diffuses and penetrates from the fiber surface to the interior of the fiber, enters the amorphous zone of the fiber, and reaches the dye solution, fiber surface and interior of the fiber. concentration reaches equilibrium.
3. Fixing
This is a key process for whether the dye fastness is good; the dye entering the amorphous area of the fiber is connected to the fiber macromolecules by chemical force (ionic bond or covalent bond), intermolecular attraction (van der Waals force) and hydrogen bonding, and obtains a certain The bonding fastness.
In actual dyeing, the above three stages cannot be clearly distinguished. Different dyes, different fibers, different dyeing processes, the dyeing process is also different.
Dyeing method
1. Direct dye dyeing
Direct dyes are generally soluble in water because they contain water-soluble groups in their molecular structure. There are also a few dyes that require the addition of some soda ash to help dissolve them. They can directly dye fibers such as cotton, linen, silk, wool, and viscose without relying on other additives, so they are called direct dyes. Adding neutral electrolytes such as salt during dyeing can increase the amount of impurities on the dye. Direct dyes have complete chromatograms, bright colors, low prices, simple dyeing methods, and uniform color production. However, their color fastness to washing and sunlight are poor. Except for light colors, color fixation is generally required.
2. Reactive dye dyeing
Reactive dyes refer to soluble dyes containing reactive groups. The molecules contain one or more reactive groups (also called 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 low color fixation rates 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 dye dyeing
Vat dyes (trade name Shilin dyes) are insoluble in water and cannot be dyed directly. During dyeing, they must be reduced and dissolved in an alkaline reducing solution to form leuco sodium salts before they can be dyed on the fiber. After oxidation, they can be converted back into The original color lake is fixed on the fiber.
Vat dyes have a complete chromatogram and bright colors. They are dyes with excellent properties in all dyes, especially light fastness and washing fastness that are inferior to other dyes. However, they are more expensive, have fewer red varieties, and can dye strong colors. The color fastness to rubbing is poor, and some yellow-orange dyes are photosensitive and brittle, so their use 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. Dyeing with soluble vat dyes
Soluble vat dyes, also known as indycotin dyes, are mostly derived from vat dyes. Soluble vat dyes are soluble in water and have a certain affinity for cellulose fibers. The dyeing process of soluble vat dyes is relatively simple. The dye has good diffusion and leveling properties, high color fastness to rubbing, and good color fastness to sunlight, washing and perspiration. However, this dye is expensive and is mainly used for dyeing and printing of light and medium-colored cotton fabrics.
5. Sulfur dye dyeing
Sulfur dyes contain sulfur, which cannot be directly dissolved in water, but can be dissolved in sulfide alkali and reduced to a leuco body. After being absorbed by the cotton fiber, the leuco body is oxidized into an insoluble dye and fixed on the cotton fiber, so it is called Sulfur dyes. Sulfur dyes are mainly used for dyeing dark-colored cotton fiber products. The washability and sun exposure are good. Sulfur dyes are simple to manufacture, low in price, simple in dyeing process, easy to match colors, and have good dye fastness. However, the chromatogram is not complete and is mainly blue. Mainly black, the color is not bright. Some dyes (such as sulfur black) will make the fibers brittle during the storage of the fabric, so anti-brittle treatment is required after dyeing. Yellow and orange sulfur dyes often cause photosensitive brittleness to fibers.
6. Acid dye dyeing
Acid dye molecules contain acidic groups such as sulfonic acid groups and hydroxyl groups, which are easily soluble in water and ionize into dye anions in aqueous solution. Acid dyes have bright colors, complete chromatograms, simple dyeing processes, and easy color matching.
7. Disperse dye dyeing
Disperse dyes are a type of nonionic dyes with small molecules, simple structures, and no water-soluble groups, so they are difficult to dissolve in water. When dyeing, they need the help of a dispersant to make them evenly dispersed in the dye in the form of fine particles. In liquid, it is called disperse dye. Disperse dyes have a complete chromatogram, a wide variety of varieties, good hiding properties, and a wide range of uses. They are especially suitable for dyeing polyester, acetate fiber, nylon, etc.
8. Cationic dye dyeing
Cationic dyes are developed on the basis of original basic dyes. They are water-soluble dyes with very rich colors. They can be ionized in solution to generate pigment cations and simple anions. They are special dyes for acrylic fibers containing acidic groups.