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Wind print generally refers to a kind of dyeing defects produced during drying and storage of dyed and processed textiles. Compared with normal dyed blanks, windprints appear white or shaded gray strips in almost the entire width of the web. This defect can not be seen before stereotypes, and it will occur after stereotypes.
Polyester fabrics are not prone to wind prints during continuous production (long car production lines) , but intermittent production (during high temperature and high pressure dyeing) can easily produce wind prints. Most of the prints of polyester fabrics occurred after the dehydration of the cloth and before the finalization of the fabric, which occurred when the cloth was stored on the stacker. In severe cases, dozens of lines appear in the zonal direction, and the spacing is exactly the spacing of the reciprocal folds of the grey cloth .
The reason why the non-slurry polyester woven fabric or knitted fabric produces wind print
After the opening of the fabrics is to be determined, the reciprocating folds are exposed to the air, and the air flow causes the moisture of these parts to volatilize and air dry first. Due to the capillary effect, free water from other areas will flock toward the reciprocating fold. However, antistatic agents and lubricants added during spinning and weaving, and leveling agents and detergents added after dyeing, will still remain in the free water carried by fabrics and fabrics. Most of these additives are Non-ionic additives. As with the principle of dye migration, when free water is poured into the reciprocating fold, the residual agent dissolved in free water is also flocked to the reciprocating fold.
As the moisture evaporates further, the concentration of the auxiliaries at the reciprocating folds is much greater than at other sites. In the high-temperature shaping process, the thermal migration of the disperse dyes produced by the reciprocating folding sites is significantly greater than other sites. The reason for the thermal mobility of disperse dyes is that the auxiliaries of the fiber outer layer can produce dissolution at high temperatures. The dye migrates from the inside of the fiber to the surface layer of the fiber through the capillaries, causing the dye to accumulate on the surface of the fiber and cause a series of effects. Such as color light changes, friction, washing, perspiration, dry cleaning, light fastness and other color fastness. However, the fatal effect is the difference in the serious shade between the reciprocating fold and other normal parts, namely the wind print.
The reason why the sizing polyester woven fabrics produce wind prints
Compared with the non-pulp polyester woven fabric or knitted fabric, the sizing polyester woven fabric dyeing and finishing process takes a long time, and most of the auxiliary agents used in spinning and weaving have been removed. However, auxiliaries used in the dyeing and post-treatment processes may still remain in the fabric and the free water it carries. In addition, although two hot and one picklings have been passed after desizing, the caustic soda used in desizing may still remain in small amounts inside the single fiber of the polyester fiber or even inside the amorphous region.
Similarly, free water can carry residual alkali and additives to the reciprocating fold during the stacking process before the fabric is set. At this point, the alkaline pH at the reciprocating fold is significantly higher than other parts of the fabric. This is also confirmed by the use of the universal indicator. The concentration of the auxiliary is also greater than other parts. During the high-temperature shaping process of the fabric, the polyester macromolecular chains move vigorously, and the OH- ions can react with the disperse dyes as the water molecules instantaneously drill into the amorphous region.
Disperse dyes under acidic conditions (pH value 5) were stable under basic conditions to disperse generally the following two effects: alkaline conditions dissociation of certain dyes can structure, this reaction is reversible, neutral Or the slightly dissociated structure reappears in the slightly acidic structure. Alkali can hydrolyze some disperse dyes. After hydrolysis, the dye not only changes color, but also has different affinity. Alkali can therefore permanently damage certain disperse dyes.
Therefore, the sizing of the sizing polyester woven fabric at the reciprocating fold is caused by a combination of high pH values, hydrolysis or dissociation of the disperse dyes, and thermal migration of the disperse dyes.
Ways to Avoid the Printing of Polyester Fabrics
If the above two kinds of fabrics can be dehydrated, opened, and shaped in a timely manner after being discharged from the cylinder, generally no wind print will be produced. If placed for a period of time (about 30 hours) and then stereotypes are easy to produce wind marks. If we want to fundamentally solve the problem, we must start from the mechanism of creating wind and print, and minimize the factors that produce wind prints.
The reason why textiles produce wind marks is mainly related to dyes. In general, a small number of vat dyes, naphtol dyes, and partially vinyl sulfone reactive dyes, and most direct dyes, can produce wind prints because the dye itself has poor fastness to sunlight and oxidation. Certain reactive dyes have strong sensitivity to alkalis. If the alkalinity of the cloth is not completely removed after dyeing, it will easily produce wind prints when the pH value is greater than 8 (such as active Cuilan KN-G, reactive brilliant orange G, etc.).
Stereotype found windy, while the remaining unshaped fabric reciprocating folds at high concentrations of additives or OH- ions, but the physical adsorption on the surface of the fiber, can not dissolve the amorphous area of ​​the dye without high-temperature forming aids, OH- ions Also unable to enter the amorphous region of the fiber reacts with the disperse dye. Therefore, after washing or pickling, the high-concentration additives and OH- ions in the reciprocating folds have been diluted, and re-setting in time can avoid wind prints.
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