Dyeing Methods with Commonly Used Dyes

Direct dye dyeing

Direct dyes can be used for dyeing various cotton and viscose products. When dyeing, first wet the fabric with water, add it to the dye solution, heat it to 95°C, add neutral salt to promote dyeing, and dye it for 60 minutes. Wash with water after dyeing, and if necessary, add color fixing agent to improve the dye fastness. Silk dyeing often uses direct dyes with high dye uptake and good color fastness to supplement the shortcomings of acid dye chromatography, mainly in brown, black, dark green and other colors. Dyeing can be carried out in a neutral or slightly acidic bath. Salt is often added to promote dyeing. After dyeing, the hand feel can be improved. It can be treated in a dilute acetic acid bath for a period of time.

Vat dye dyeing

Vat dyes have bright colors, complete chromatograms and good color fastness. They are high-grade dyes used for dyeing cellulose fibers. There are two different processes for vat dyeing: colorless exhaust dyeing and suspension pad dyeing.

When colorless dip dyeing, first use insurance powder (a strong reducing agent) and caustic soda to reduce the dye to a colorless body and dissolve it in a soda ash solution, then put it into the dyeing material, control the temperature, and adjust the amount of salt to ensure dyeing. Rate. After dyeing, it must be oxidized to fix the colorless body on the fiber, and finally soaped to improve the color light of the dyed product and increase the color fastness.

In suspension pad dyeing, the dye is not reduced and is prepared into a dispersion of suspended fine particles, dip-dyed on the fabric, then dried, dip-dyed and pad-dyed in an alkaline reducing solution containing insurance powder, and then entered into a closed steam engine for promotion Reduction, dissolution, diffusion and penetration of dyes, and finally oxidation and soaping. The most commonly used vat dye at present is indigo, which is mainly used in the processing of denim fabrics and clothing.

Sulfur dye dyeing

Sulfur dyes are commonly used to dye cotton textiles into deep black and blue colors. The dyeing method is similar to that of vat dyes. The dye is first reduced and then dissolved, and then oxidized to develop color after dyeing. The reducing agent here is usually sodium sulfide, which is more easily oxidized than vat dyes. Taking cotton roll dyeing as an example, the fabric is dyed at high temperature for a period of time in a dye hidden bubble solution, then washed and oxidized, and finally treated with sodium acetate to resist brittleness.

Reactive dye dyeing

Reactive dye molecules contain reactive groups, which can react with certain groups on the fiber to form covalent bonds. They have high color fastness to washing and rubbing, and can be used for dyeing cellulose fibers, wool, silk, nylon, etc. .

Dyeing of cellulose fibers: In the process of dip dyeing and pad dyeing, the fabric is usually treated with an alkali-free dye liquor, and then alkali is added to the dye liquor or to the fabric to react the dye with the dye. The fiber is, finally, thoroughly washed, soaped and boiled to remove any floating color.

Wool, silk, nylon dyeing: Wool dyeing is usually carried out under acidic conditions, using acetic acid to adjust the PH value, using Yuanming powder as a retarder, neutralizing, and washing with water after dyeing. Silk can be dyed in weak acidic and neutral dyeing or alkaline conditions through different processes, or dyed first in a weak acidic or neutral bath and then fixed in an alkaline bath. Nylon has fewer reactive groups than wool and silk, so it is difficult to dye dark colors with reactive dyes. The dyeing process is similar to silk.

Acid dyes, acid mordant dyes, acid mordant dyes for dyeing

These three dyes are all water-soluble and specifically used on wool, silk and nylon, but they have certain differences in structure, performance and application range.

Acid dyes have a simple structure and can be divided into two categories: strong acid dyes and weak acid dyes according to the size of their molecular structures. Strong acid dyes can dye wool in strong acidic media with bright colors and good uniformity. Weak acid dyes can dye wool, silk, and nylon in neutral or weakly acidic media with high color fastness, but the uniformity and brightness are not as good as Strong acid dye.

Acid mordant dyes have the basic structure of acid dyes, but also contain groups that can form complexes with mordant chromium ions. These dyes are mainly used for wool dyeing and have better color fastness to washing and sunlight than acid dyes, but the color is darker. Dyeing often uses the dip dyeing method, and potassium dichromate is used as a mordant for a period of time after dyeing.

Dyes containing acid mordants are easy to apply because they do not require a mordant for dyeing. When chromium ions are complexed with dye molecules at a ratio of 1:1, the dyeing effect is similar to that of strong acid dyes, and it is mainly used for wool. When chromium ions are complexed at a ratio of 1:2, the dyeing effect is higher, but the color is darker and is commonly used. Neutral bath dyeing for wool, silk and nylon.

Disperse dye dyeing

Disperse dyes are the main dyes used for dyeing synthetic fibers, especially polyester fibers. They have good dyeing properties and high color fastness to polyester.

Disperse dyes do not contain ionizing genes in their structure and are non-ionic hydrophobic dyes that are insoluble in water and can only be suspended in the dye solution in the form of particles. Disperse dyes have a simple structure and small molecules. They have affinity for hydrophobic polyester fibers with a tight structure and can diffuse into the fiber, resulting in a high dye uptake rate.

Disperse dyes have a simple structure and small molecules. They have affinity for hydrophobic and tightly structured polyester fibers, allowing them to diffuse into the fiber and have a high dye uptake rate. When dyeing polyester with disperse dyes, high temperature conditions above 120°C are required, because only at high temperatures can the degree of thermal movement of polyester macromolecular chains be sufficient to create the gaps required for dye diffusion.

There are three types of disperse dyes for polyester dyeing: carrier method, high temperature and high pressure method, and hot melt method. High temperature and high pressure (HTHP) method is the most commonly used method. Dyeing is carried out in a closed high-pressure container, the temperature can reach up to 130°C, and the dye uptake rate is high. Acetic acid and leveling agent can be added to assist the dyeing to control the color light and dyeing. Uniformity of dyeing.

Cationic dye dyeing

Cationic dyes are the main dyes for acrylic fiber dyeing. They not only have bright colors, high dye uptake rates, but also good color fastness. Because acrylic fiber macromolecules contain acidic groups, which become negatively charged after ionization in water, they have strong adsorption capacity for cationic dyes, fast dyeing speed, and high dye uptake rates.

Cationic dyes have poor dye migration on acrylics. Due to the fast dyeing speed, uneven dyeing is prone to occur, so the dyeing process must be strictly controlled and the dyeing agent must be used. Commonly used dye migration agents include acetic acid, methylamine powder, cationic surfactants, etc. Dyeing generally uses the dip dyeing method, using acetic acid, etc. to adjust the pH of the dye solution to 4.5, and adding a dye migration agent. Starting from room temperature, the temperature rise rate is strictly controlled and dyeing continues for a period of time. After boiling for a certain period of time, then slowly cool and wash. There are also modified polyester fibers that can be dyed with cationic dyes.

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