Why are there horizontal stripes in nylon dyeing?

Nylon is the trade name of synthetic polyamide fiber, commonly known as nylon. Its basic composition is aliphatic polyamide connected by amide bond -NHC0. The nylons commonly used in textile fabrics include nylon 6 and nylon 66. Nylon macromolecules are mainly composed of three parts, namely the hydrophobic methylene part, the hydrophilic amide group and the amino and carboxyl groups at the chain end. Although the amino content of nylon is low, its molecular chain has a large number of methylene groups that can form van der Waals forces and hydrogen bonds with dyes, so nylon can be combined with anionic dyes in the form of ionic bonds. Van der Waals forces interact with dyes to color. Although nylon 6 and nylon 66 have some small differences in molecular structure and dyeing properties, their dyeing and finishing processes are the same.

Nylon fiber has been widely used in clothing fabrics, high-end underwear, sportswear and mountaineering clothes because of its good strength, excellent wear resistance, better hygroscopicity than polyester fiber, and better wearing comfort than polyester clothing. Due to the development of the market and the advancement of spinning technology, elastic fibers (spandex yarn) are added to most nylon fabrics to enhance the abrasion resistance and resilience of nylon fabrics, which increases the difficulty of dyeing and finishing of nylon fabrics.

Cause Analysis:

Nylon fibers on fabrics differ in chemical or physical characteristics:

(1) Physical differences in yarns, including differences in yarn count, number of fibers in the yarn, or denier of fibers, and the difference between the end crimp of a single fiber in the yarn or the difference between the end crimps of multiple fibers.

(2) The chemical difference comes from the difference in the amino group content of the fibers, which may be generated during the spinning process, the thermal drawing process, or the filament doubling process. For example, the inhomogeneity of the supramolecular structure produced by the nylon fiber during the treatment process, such as the difference in the degree of crystallinity and orientation in the fiber, or the inhomogeneity of the skin-core structure, etc.

 Solution:

(1) Strengthen the detection of grey fabrics, and choose light color, natural white or brightened white for different choices.

(2) Choose dyes with good coverage and levelness. The coverage and levelness of disperse dyes are better than those of acid dyes, and some disperse dyes can be optionally added.