Generally, after completing a series of pre-treatments, fabrics enter the dyeing process. The purpose of dyeing is to color the natural fabric with the various colors we envision.
This process involves many factors, but the most basic principle is to use specific dyes and additives with water as the medium, under specific conditions (such as a certain temperature and pH value) after a certain period of time, the dye migrates to the fiber, penetrates and finally combines. The entire process of dyeing is explained in detail below with specific examples.
Polyester (polyester) fiber
Polyester fiber is dyed with disperse dyes. The fiber itself has no reactive groups, so the requirements for dyeing conditions are relatively high. That is, at high temperatures, the polyester fiber molecular chains move and increase the space inside the fiber, allowing small dye particles to enter the inside of the fiber and coexist with it. The form of the valence bond is combined and fixed.
This process needs to provide enough capacity to make the polyester fiber molecular chain move, that is, the temperature needs to reach 130°C. At the same time, glacial acetic acid and bath softener need to be added to the dye bath. , leveling agent, diffusion agent (dispersant) to coordinate the entire process.
1. The function of glacial acetic acid is to adjust the pH value (i.e. acidity and alkalinity) of the dye bath to make it slightly acidic to increase the solubility and permeability of disperse dyes, making dyeing easier. .
2. The role of the softener in the bath is to soften the fabric during the dyeing process and prevent surface defects such as creases and chicken paw prints.
3. The function of the leveling agent is to adjust the distribution balance rate between the dye and the fabric during the dyeing process to achieve a leveling effect.
4. The function of the diffusing agent is to help disperse dyes to disperse evenly in the dye bath and prevent the aggregation of disperse dyes to cause color spots.
What should be considered when dyeing polyester fiber is the sublimation fastness of disperse dyes. The so-called sublimation is a process that directly changes from a solid to a gas under thermal conditions. Since the polyester fiber and the dye have no reactive groups to fix, the dye will sublimate due to high temperature during the setting process, resulting in a lighter color; Therefore, when dyeing polyester with disperse dyes, the sublimation fastness of the dye must be considered. The dye is generally selected according to the final requirements.
Since dyeing occurs under high temperature conditions, and the movement of polyester fiber molecular chains requires a lot of energy, the wash fastness of polyester after dyeing is quite high and is not considered. However, for dark colors such as extra black, due to the large amount of dye, it cannot completely enter the inner space of the fiber and be fixed. There will be excess dye adsorbed on the surface of the fiber after dyeing. If it is not removed cleanly, it will affect the washing fastness. , so soaping and washing must be done after dyeing.
The so-called soaping is to use detergent and soda ash at a certain temperature to elute the dye adsorbed on the fiber surface, and wash it thoroughly to ensure the wash fastness of the fabric.
Nylon (nylon) fiber
The dyeing of nylon fiber mainly uses acid dyes and some disperse dyes . Disperse dyes are mainly used in lighter colors, and acid dyes are the most commonly used. Acid dyes are divided into leveling acid dyes (strongly acidic acid dyes); semi-leveling acid dyes (weakly acidic acid dyes) and neutral dye.
The basis for the selection of dyes is the depth of the color:
1. Light color: disperse dyes and leveling acid dyes;
2. Medium and dark colors: semi-level dyeing acid dyes;
3. Dark colors: neutral dyes;
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For those with particularly high requirements on wash fastness, metal complex dyes are used. (Rarely used) The principle of dyeing nylon with acid dyes is that the dye and fiber are combined by covalent bonds and van der Waals forces in the acid bath and are fixed on the fiber after fixation. Dye conditions are certain temperature, pH value and leveling agent.
The following is a process statement on different dyes:
1. Level dyeing acid dyes: also called strong acidic acid dyes. It means that it needs to be dyed under strong acidic conditions, and glacial acetic acid is added to promote dyeing. It is characterized by excellent level dyeing but poor wash fastness. Therefore, color fixation must be carried out to achieve a certain fastness.
2. Semi-level dyeing acid dyes: also called weakly acidic acid dyes, which refer to dyeing under weakly acidic conditions. Since the fastness of such dyes after combining with fibers is acceptable, the amount of glacial acetic acid needs to be well controlled, and the addition of leveling agents is also very important to prevent color differences and color blooms caused by too fast dyeing speed.
3. Neutral dyes: They need to be dyed under near-neutral conditions. Since these dyes are not easy to fall off again after being combined with the fiber, the amount of glacial acetic acid is rarely or even not used. , and the addition of leveling agent is particularly important. The leveling agent acts as a dye retardant.
Except for disperse dyes, which generally do not undergo fixation treatment, nylon fibers dyed with acid dyes generally need to be fixed with fixatives to improve wash fastness. In general, what needs to be considered when dyeing nylon fiber is the combination of acid dye types and their washing fastness. Process control uses different methods based on different dyes.
For acid dye nylon fibers, a very important issue is the impact of water quality, especially some heavy metal ions such as Fe and Mn. Their presence will cause changes in the color of the light – ���Dark.
Therefore, the water used to dye nylon with acid dyes needs to undergo ion exchange, that is, the process in which Na ions replace some heavy metal ions such as Fe and Mn after passing through the ion exchanger.
Since the dyeability of nylon fiber is greatly affected by heat, the uniformity of heating of nylon fiber during the pre-treatment process will affect the uniformity of dyeing. This is particularly important in the dyeing of fibers there. The dyeing processes described above all occur in the dye vat. Therefore, it is necessary to give a rough explanation of the structure and operation of the dye vat, mainly taking the high-temperature and high-pressure overflow dyeing machine as an example. </p
