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Dyeing of polyester fiber uses disperse dyes. Since the polyester fiber itself has no reactive group, the dyeing conditions are relatively high. Under the condition of high temperature, the molecular chain of polyester fiber moves and increases the space inside the fiber, so that the fine dye particles can enter the inside of the fiber and bond in the form of covalent bond and fixation. This process needs to provide sufficient capacity to make the molecular chains of polyester fiber move, that is, the temperature needs to reach 130℃. At the same time, glacial acetic acid, bath softener, evenly dyeing agent and diffuser (dispersant) need to be added in the dyeing bath to coordinate the whole process.
1 The role of glacial acetic acid is to adjust the pH value of the dye bath to be slightly acidic to increase the solubility and permeability of disperse dyes and make dyeing easier.
2 The purpose of the bath softener is to provide a soft effect on the fabric during the dyeing process without causing fabric defects such as creases and chicken footprints.
3 The role of leveller is to adjust the distribution balance between dye and fabric during dyeing to achieve levelling effect.
4 The role of the diffuser is to help disperse dyes evenly dispersed in the dye bath, to prevent the condensation of disperse dyes resulting in color spots this defect.
The sublimation fastness of the disperse dye is considered in the dyeing of polyester fibers. Sublimation is the process by which a solid is changed directly into a gas under the condition of heat. Because there is no reactive group fixed between polyester fiber and dye, the dye will sublimate due to high temperature in the shaping process, leading to the phenomenon of lighter color. Dyeing polyester with disperse dyes must consider the sublimation fastness of the dye.The dye is generally selected according to the final requirements.
Since dyeing occurs at high temperature and the movement of polyester fiber molecular chains requires a lot of energy, the washing fastness of polyester fiber after dyeing is quite high, which is not considered.
However, for dark colors such as extra black, due to the large amount of dye, it cannot completely enter the internal space of the fiber and fixate. After dyeing, excess dye will be adsorbed on the fiber surface. If it is not removed clean, it will affect the washing fastness, so it must be soapy and washed after dyeing.
Soaping is to elute the dyes adsorbed on the fiber surface with detergent and soda at a certain temperature, and wash with water to ensure the wash fastness of the fabric.
Nylon fibers are dyed mainly with acid dyes and partially disperse dyes.Disperse dyestuff is mainly used in relatively light color, and the most used is acid dyestuff, acid dyestuff leveling acid dyestuff (strong acid dyestuff);Semi-leveling acid dyes (weak acid acid dyes) and neutral dyes.
The choice of dye is based on the depth of the color:
1 Light colors: disperse dyes and leveling acid dyes;
2 Medium dark color: semi-leveling acid dye;
3 Dark color: neutral dye;
Metal complexing dyes are used for those requiring particularly high wash fastness.(rarely used) the principle of acid dye dyeing nylon is in the acid bath dye and fiber covalent bond and van der Waals force combination and after fixing, fixed on the fiber and coloring.Dye conditions are certain temperature, pH value and leveler.
The following is a process statement for different dyes:
1 Level-dyeing acid dyes: also known as strong acid acid dyes, that is, the need to dye under the conditions of strong acid, adding glacial acetic acid from the effect of promoting dyeing.It is characterized by excellent levelness but poor wash fastness.Therefore, it must be fixed to achieve a certain fastness.
2 Semi-leveling acid dyestuff: also known as weak acid acid dyestuff, that is, under the condition of weak acid dyeing.Because of the fastness of these dyes to the fibers, the amount of glacial acetic acid needs to be well controlled. The addition of levellers is also important to prevent chromatic aberration and color flaking due to the rapid dyeing of dyes.
3 Neutral dyes: need to be dyed under near neutral conditions. Because this kind of dye is not easy to fall off again after combining with the fiber, so the amount of glacial acetic acid is very little or no. And the addition of levelling agent is particularly important.Levelling agents act as a retarding effect.
In addition to disperse dyes are generally not fixed color treatment, acid dyes dyed nylon fibers generally need to be fixed color by fixing agent to improve the wash fastness. In general, the dyeing of nylon fibers should consider the combination of acid dyes and their wash fastness.The process is controlled by different methods according to different dyes. For acid dye nylon fiber, a very important problem is the influence of water quality, especially Fe, Mn and other heavy metal ions, their existence will lead to the color of the light change - dark.
Therefore, the water dyed with acid dye nylon needs ion exchange, that is, through the ion exchanger after Na ions replace Fe, Mn and some other heavy metal ions process.
Because the dyeing property of nylon fiber is greatly affected by heat, the uniform degree of heating of nylon fiber in the pretreatment process will affect the uniform degree of dyeing.This is particularly important in the dyeing of the fibers there.The dyeing process described above all takes place in the dye VAT, so it is necessary to make a general explanation of the structure and operation of the dye VAT, mainly taking the high temperature and high pressure overflow dyeing machine as an example.
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