The troublesome fastness problem of spandex: Dark dyeing of polyester and spandex varieties often suffers from quality problems such as staining or inconsistent washing fastness. In particular, fabrics used for white clothing have higher requirements for color fastness. Therefore, how to further improve the fastness of dark-colored polyester and polyurethane fabrics has always been the focus of dyeing factories. Now we will briefly discuss the process or operation for reference by peers.
The main reason for the decrease in the fastness of polyester and spandex is that spandex itself has a certain degree of hydrophobicity, and disperse dyes can dye it to a certain extent. Moreover, its glass transition temperature is lower than that of polyester, resulting in ordinary dispersion. There is a phenomenon that dyes can stain spandex easily but can also be easily desorbed and seriously stain spandex. This staining varies in severity depending on the structure of the disperse dye, which leads to staining on the spandex during post-dyeing finishing such as heat and humidity setting and during the consumption process. The dispersion material will migrate out of the fiber and eventually cause a decrease in fastness.
Measures taken
1. Strengthen pre-treatment to remove oil. Polyester and spandex fabrics contain a lot of spinning and weaving oils and silicone oil for spandex. You should choose an emulsifying degreaser with both dispersing, emulsifying and degreasing capabilities to ensure sufficient degreasing, otherwise the oil will not be removed or dispersed. It will affect the fixation of the dye or combine with the dye to cause a series of quality problems such as color spots and poor fastness. For those with high spandex content, the dyeing and oil removal bath process should be adopted. If necessary, it can also be rolled 2-2 times in the previous process. 3g/L emulsifier to prevent the oil from forming conjunctiva due to high temperature, making it more difficult to remove later.
2. In the dyeing process, try to use a higher dyeing temperature without affecting the strength of the spandex, and at the same time keep it warm for an appropriate time, such as 130℃×20′, to disperse the stain on the spandex. The dye migrates to the polyester to the maximum extent through contact transfer. The dyeing temperature of 120-125°C in the conventional process will cause incomplete and insufficient dyeing of the disperse dye, which will also increase the floating and staining of the disperse dye. Adversely affects color fastness.
3. When choosing dyes, try to use disperse dyes with high fastness. This type of dye has good heat migration resistance and high temperature sublimation resistance. At the same time, unfixed dyes are relatively easy to clean, such as Ciba’s 3W series, Dystar’s XF series, Longsheng’s HW and Runtu’s SF, HF types, etc. can further improve the dye fastness of the dispersion itself.
4. Strengthen reduction cleaning. The staining on the surface of spandex and the floating color of polyester fiber can only be effectively removed through reduction cleaning. It is difficult to completely remove the staining of spandex using only traditional H/S and Na2CO3. , an additive with effective anti-staining effect should be added, which can form a stable association with the washed-out floating color to avoid re-staining. At present, there are some large domestic additive suppliers of this type of additives, such as Zhejiang Chuanhua, Guangzhou Demei, etc.
5. For higher fastness requirements, two reduction cleanings can be used if necessary, that is, one reduction cleaning after dyeing, and a second reduction cleaning after high temperature setting. In this way, the dark-colored varieties after two reduction cleanings can basically guarantee that the washing and staining fastness, including white spelling fastness, can reach about level 4.
6. On the premise of ensuring the weight and shrinkage of the final finished product, mild process conditions should be adopted, such as 150-160°C, especially for fine denier or ultra-fine fibers, which can be more effective. Reduce the thermal migration of dyes and further improve color fastness.
Practice has shown that through the improvement and strengthening of the above processes, the fastness of dark polyester and ammonia varieties can be significantly improved, and it can fully meet or meet the customer’s fastness requirements. </p
