Cotton knitted fabric is a common fabric for dyeing and finishing. Let’s take a look at the dyeing methods and processes of cotton knitted fabrics using direct dyes, reactive dyes and sulfur dyes.
Direct dye dyeing of cotton knitted fabric
1. Characteristics of direct dyes
1. Direct dyes are a type of fiber that can be dyed directly in a neutral dye bath. Water-soluble dyes for plain fibers.
2. Direct dyes have a complete chromatogram, are easy to apply, are cheap, and have poor washing fastness and poor light fastness. Fixing agent treatment is often required.
2. Dyeing properties and methods of direct dyes
1. Dyeing properties
1.1 Direct dyes are all soluble in water, and the solubility increases significantly with the increase of temperature.
1.2 Direct dyes Commonly used dye accelerators in dyeing are salt and Yuanming powder. Using Yuanming powder as a dye accelerator can produce brighter colors.
1.3 Direct dyes are not resistant to hard water and must be dyed with soft water.
2. Dyeing method
2.1 It is generally carried out on an ordinary rope dyeing machine, and the dyeing bath ratio The liquor ratio of light colors is 1:15-30, which is larger than that of dark colors.
2.2 The dyeing temperature is generally near the boiling point to obtain good dye migration (the so-called dye migration refers to the diffusion of dye from high concentration to low concentration on the fiber) and Good shade and fastness. Dyeing usually starts at room temperature (for dark colors, it can start at 60℃-80℃).
3. Fixation treatment of direct dyes
1. Utilization Cationic fixing agent, treated with fixing agent Y and fixing agent M to improve its fastness.
Reactive dye dyeing of cotton knitted fabrics
1. Characteristics of reactive dyes
1. Reactive dyes can be dissolved in water and contain active genes in their molecular structure. Under certain conditions, they can form covalent bonds with the hydroxyl groups on cellulose fibers.
2. Reactive dyes have bright colors, good wet processing fastness and rubbing fastness, good level dyeing, relatively uniform chromatography, easy application, and good light fastness. .
2. Some main factors affecting reactive dye dyeing
1 , The influence of affinity
1.1 When dyeing with a dye with a high affinity, it has a relatively high dyeing percentage, which is beneficial to improving the utilization rate of the dye, but washing must be strengthened. Otherwise, it will affect the washing and rubbing fastness of dyed goods.
2. The influence of liquor ratio
2.1 When dyeing with reactive dyes, the bath ratio should be reduced as much as possible without affecting level dyeing. This not only improves the fixation rate, but also reduces the hydrolysis of reactive dyes in the dye bath.
3. Influence of temperature
3.1K type reactive dyes need to be used at higher temperatures Dyeing at temperature.
X-type reactive dyes can promote the hydrolysis of dyes as the temperature increases, so they cannot be dyed at high temperatures.
3.2 Influence of alkali agent: In order to ensure color fixation, use a lower pH as much as possible. Generally, it is appropriate to control the pH at 10-11.
3.3 Influence of electrolytes: Reactive dye molecules are small, have good diffusion properties, and have good leveling effects. Therefore, adding a larger amount of electrolytes can promote dyeing.
Sulfur dye dyeing of cotton knitted fabrics
1. Sulfur dyes Characteristics
1. Sulfur dyes are cheap, easy to apply, and suitable for dyeing various cellulose fiber products.
2. The color of sulfur dyes is not bright, the fastness to chlorine is poor, the chromatogram is incomplete, and it has a brittle effect on the fiber. The sun fastness varies greatly with different varieties. Generally, black is 6- Level 7, blue is level 4-5, yellow and orange is level 3-4, soaping fastness, most can reach level 3-4.
2. Post-processing of sulfur dye dyeing
1. Soap Washing treatment: remove the floating color attached to the fiber surface, improve the dye fastness and enhance the color brightness of the dyed goods.
2. Taikoo oil treatment: Taikoo oil treatment of dyed materials can improve the color and light of the dyed materials, especially increase the blackness of vulcanization, and also has a certain anti-brittle effect.
3. Color fixing treatment: Color fixing agent M is commonly used for color fixing treatment.
4. Anti-brittle treatment: Some sulfur dye dyes will become brittle if left for a long time, seriously reducing the fiber strength. Anti-brittle treatment, usually 0.8-1% urea and 5-5.8% Taikoo oil.
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