Causes of fabric wind marks and how to avoid them
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Wind marks generally refer to a coloring defect that occurs during the drying and storage process of printed and dyed fabrics. Compared with the normally painted and finished area, the wind-marked area will show white or dark gray long strips in the latitudinal direction of almost the entire width of the door. This defect is not visible before setting, but will appear after setting.
Polyester fabrics are not prone to wind marks during continuous production (long car production lines), but are prone to wind marks during intermittent production (high temperature and high pressure overflow coloring). Wind marks on polyester fabrics mostly occur after the fabric is dehydrated and opened and before it is set, and appear in the reciprocating folding marks when the fabric is stored in the stacker. In severe cases, dozens of strips will appear in the weft direction, and their spacing is exactly the spacing of the natural cotton cloth being folded back and forth.
The reasons why sizing-free polyester woven fabrics or knitted fabrics produce wind marks
When this kind of fabric is laid out after opening, the reciprocating folds are exposed to the air, and the flow of air causes the moisture in these parts to evaporate and dry first. Due to the capillary effect, free water in other parts will flow towards the reciprocating folds. However, the antistatic agents, lubricants added during spinning and weaving, and the leveling agents and cleaning agents added during post-coloring processing will still have a small amount of residues in the fabric and the free water carried by the fabric. Among these additives Most are non-ionic additives. Similar to the principle of dye migration, when free water flows to the reciprocating folding point, the residual additives dissolved in the free water also flow to the reciprocating folding point.
As the water further evaporates, the concentration of additives in the reciprocating folds is much greater than in other parts. During the high-temperature setting process, the thermal migration (thormo-migration) of disperse dyes produced in the reciprocating folding parts is significantly greater than that in other parts. The reason for the thermal migration of disperse dyes is that the additives in the outer layer of the fiber can dissolve at high temperatures. The dye migrates from the inside of the fiber to the surface of the fiber through capillaries, causing the dye to accumulate on the surface of the fiber, causing a series of effects. Such as color change, friction, washing, sweat stains, dry cleaning, light fastness and other decreases in dyeing fastness. But the fatal effect is the serious color difference between the reciprocating fold and other normal parts, that is, the wind mark.
The reasons why sizing polyester woven fabrics produce wind marks
Compared with sizing-free polyester woven fabrics or knitted fabrics, the dyeing and finishing process of sizing polyester woven fabrics takes a long time, and most of the additives used in spinning and weaving have been removed. However, the additives used during coloring and post-treatment may still remain in small amounts on the fabric and the free water it carries. In addition, although it has been hot washed twice and pickled once after desizing, a small amount of caustic soda used during desizing may still remain inside the single fibers of the polyester fiber or even inside the amorphous zone.
Similarly, during the process of stacking fabrics before they are set, free water can carry residual alkali and additives and flow to the reciprocating folds. At this time, the pH value of the reciprocating folds was significantly higher than that of other parts of the fabric. This was also confirmed with a universal indicator, and the concentration of the additive was also greater than that of other parts. During the high-temperature setting process of fabrics, the polyester macromolecular chains relax violently, and OH- ions can instantly penetrate into the amorphous zone with water molecules and react with disperse dyes.
Disperse dyes are relatively stable under acidic conditions (pH value 5). Alkaline conditions generally have the following two effects on disperse dyes: Alkaline conditions can dissociate the structure of some dyes. This reaction is reversible. Or undissociated structures may reappear in slightly acidic structures.
Alkali can hydrolyze certain disperse dyes. After hydrolysis, the dyes not only change color, but also have different affinities. Therefore, alkali can permanently damage some disperse dyes.
Therefore, the discoloration at the reciprocating folds of sized polyester woven fabrics is caused by excessive pH value, hydrolysis or dissociation of disperse dyes, and the combined effect of thermal migration of disperse dyes by additives.
Methods to avoid wind marks on polyester fabrics
If the above two kinds of fabrics can be dehydrated, opened and shaped in time after coming out of the vat, they will generally not produce wind marks. If left for a period of time (about 30 hours) before shaping, it is easy to produce wind marks. In order to fundamentally solve the problem of wind marks, we must start from the mechanism that produces wind marks and reduce the factors that cause wind marks to a minimum.
The cause of wind marks on fabrics is mainly related to dyes. Generally, a small number of vat dyes, naftol dyes, some vinyl sulfone-type reactive dyes and most direct dyes can produce wind marks due to the poor fastness of the dye itself to sunlight and oxidation. Some reactive dyes are highly sensitive to alkali. If the alkali is not removed from the cloth surface after dyeing, wind marks will easily occur when the pH value is greater than 8 (such as reactive green blue KN-G, reactive brilliant orange G, etc.) .
It is found that there are wind marks after setting, and the high concentration of additives or OH-ions in the reciprocating folds of the remaining unset fabric is only physically adsorbed on the fiber surface, and the dye and OH-ions in the amorphous area cannot be dissolved without high-temperature styling aids. It is also unable to enter the amorphous region of the fiber and react with disperse dyes.answer. Therefore, after washing or pickling, the high concentration of additives and OH-ion ions in the reciprocating folds have been diluted, and re-shaping in time can avoid wind marks.
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