Wind mark generally refers to a dyeing defect caused by the drying and storage process of textiles after printing and dyeing. Compared with the normal dyed light base, the wind mark will show white or dull gray long strips in the latitudinal direction of almost the entire door width. This defect is not visible before setting, but will appear after setting.
Produced by the wind seal Reason
01
Sizeless polyester woven fabric or Reasons for wind marks on knitted fabrics
When this kind of fabric is laid out after opening, the reciprocating folds are exposed to the air. The flow of air causes the moisture in these parts to evaporate first and dry. 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 detergents added during post-dyeing treatment will still have a small amount remaining in the fabric and the free water carried by the fabric, and most of these additives It is a non-ionic additive. 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, fold back and forth The concentration of additives is much greater than that of 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 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 color fastness decreases. But the fatal effect is the serious color difference between the reciprocating fold and other normal parts, that is, the wind mark.
02
The reasons why sizing polyester woven fabrics produce wind marks
With starch-free polyester woven fabrics or knitted fabrics In comparison, 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, small amounts of the auxiliaries used during dyeing and post-processing may still remain in 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, the stacking of fabrics before setting During the pending process, free water can carry residual alkali and additives and flow to the reciprocating folding place. At this time, the pH value at the reciprocating fold is significantly more alkaline than other parts of the fabric. This has been confirmed with a universal indicator, and the concentration of additives is also greater than that at other parts. During the high-temperature setting process of fabrics, polyester macromolecular chains move violently, and OH- ions can instantly penetrate into the amorphous zone with water molecules to react with disperse dyes.
Disperse dyes under acidic conditions (pH value 5 ) are relatively stable. Under alkaline conditions, disperse dyes generally have the following two effects: Alkaline conditions can dissociate some dye structures. This reaction is reversible and will reappear in neutral or slightly acidic structures. Dissociated structure. Alkali can hydrolyze certain disperse dyes. After hydrolysis, the dyes not only change their color, but also have different affinities. Therefore, alkali can permanently damage some disperse dyes.
Therefore, the sized polyester woven fabric reciprocates The color change at the fold is caused by the combined effect of excessive pH value, hydrolysis or dissociation of disperse dyes and thermal migration of disperse dyes by additives.
Methods to avoid wind marks on polyester fabrics
01
We need to start with the mechanism of wind marks
If the above two 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), they will be easier to shape. Wind marks are generated. If we want to fundamentally solve the wind marks, we must start from the mechanism of wind marks and reduce the factors that produce wind marks to the minimum.
The cause of wind marks on textiles is mainly related to dyes. Usually, a few vat dyes, naftol dyes and some vinyl sulfone types Reactive dyes and most direct dyes can produce wind marks due to the poor fastness of the dyes to sunlight and oxidation. Some reactive dyes are highly sensitive to alkali. If the alkali is not removed from the cloth after dyeing, , when the pH value is greater than 8 (such as active green blue KN-G, active orange G, etc.), it is easy to produce wind marks. The dyer has no boundaries
It is found that there are wind marks when setting, and the high concentration of additives or OH- ions in the reciprocating folds of the remaining unshaped fabric is only physical. Adsorbed on the surface of the fiber, the dye in the amorphous area cannot be dissolved without high-temperature styling aids, and OH- ions cannot enter the amorphous area of the fiber to react with the disperse dye. Therefore, after water washing or pickling, the high concentration of dye in the reciprocating folds The additives and OH-ion ions have been diluted, and re-setting in time can avoid wind marks.
Polyester fabric in continuous production (long It is not easy to produce wind marks (turning production line), but it is easy to produce wind marks in intermittent production (during high temperature and high pressure overflow dyeing). Most wind marks on polyester fabrics 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 reciprocating folding of the gray fabric.
