The dyeing and printing of spandex-containing textiles is more difficult than other textiles. This is because spandex is easily damaged during dyeing and printing, and because spandex has a special chemical structure and there is currently no ideal dye for it. Dyeing and printing, and when the dyeing and printing dyes of other blended and interwoven fibers are fixed, spandex is also easily contaminated.
Spandex dyeing properties
The dyes and dyeing methods used for dyeing different spandex-containing textiles mainly depend on the fibers mixed with spandex, and they are generally dyed with their commonly used dyes. However, since it contains spandex, you should also consider dyeing the spandex. As can be seen from the previous introduction to the chemical composition and structure of spandex, the composition and structure of spandex vary with the raw materials and spinning methods used, so their dyeing properties are also different.
But overall, the structural characteristics that determine the dyeing performance of spandex are as follows:
(1) The spandex molecule basically does not have ionic groups and strong hydrophilic groups, but has more hydrophobic methylene chains CH2n and fewer aryl groups (such as the benzene ring in diisocyanate), so it It is a hydrophobic fiber.
(2) During the polycondensation process, more urea groups (NHCONH) and urethane groups (OCONH) are formed in the spandex molecules; in addition, there are more ether groups (CH2OCH2) in the polyether fiber. Polyester fiber has more ester groups (OCOR), so it has a certain number of weakly polar groups, which can generate dipole forces and hydrogen bonds with related groups in dye molecules.
(3) The block copolymer structure of spandex is unevenly distributed in the fiber. The hard segment contains many polar groups, but the structure is tight and mostly crystalline, making it difficult for dyes to enter; the soft segment is a polyether chain. (or polyester chain), the structure is relaxed, even if it crystallizes, it is easy to disassemble, and the dye can easily enter, but the binding ability with the dye is weak, and the dye can easily diffuse out.
(4) The morphology and structure of spandex produced by different spinning methods are different. The spandex spun by chemical reaction method not only has chemical cross-linking, but also has the characteristics of sheath-core structure; while the spandex spun by wet spinning generally only has a certain sheath-core structure. These differences in morphological structure will also affect the dyeing properties of spandex.
(5) In order to improve the dyeing performance of spandex, co-chain extenders (such as tertiary amines) or other additives are sometimes added during preparation, so that the dyeing performance of the spandex produced is better, and it can be dyed with acid dyes or even reactive dyes ( The amount of tertiary amine added is about 25~250mmol/kg).
Based on the above structural characteristics, spandex can usually be dyed with acid dyes, neutral dyes, acid mordant dyes and disperse dyes. However, no matter what type of dye, it is necessary to screen and select dyes suitable for spandex dyeing, so as to have good dye uptake, level dyeing, brightness and fastness.
From a structural point of view, the most suitable dyes for conventional spandex dyeing are still disperse dyes. Because disperse dyes can combine with the non-ionic polar groups in spandex through hydrogen bonds and dipole forces, and can also combine with the hydrophobic composition of spandex through dispersion forces.
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