Because of the development of denim varieties, different denims also have different requirements for the quality of the yarn used. The basic requirements are as follows:
1. When selecting cotton fiber for better dyeing performance, denim manufacturers should choose cotton with better maturity and less impurities. Yarn must have good levelness and permeability. If the maturity of the cotton fiber is poor or the fiber contains dead cotton, serious uneven dyeing will be formed after the warp yarn is dyed, which will affect the shade and cause streaks or color defects.
2. In the denim weaving process, in order to obtain all the necessary stable knitting conditions for the denim style, denim manufacturers generally choose a larger upper machine tension and need to withstand multiple open stretches. Therefore, the warp yarns are required to have higher strength and excellent elasticity.
3. Denim weft yarn evenness and yarn defects are more stringent than warp yarns. When the unevenness of the weft yarn is large or there are many slub yarn defects, the yarn strength will be low and the strength unevenness will be large, which will seriously affect the fabric style and appearance quality of the denim. When the weft yarn has serious slubs, there will be faintly visible nodular white marks on the cloth surface, which is detrimental to the unique style of "blue and white" on the denim surface. Therefore, denim manufacturers require the yarn to be evenly even and with few defects.
4. Yarn hairiness should be less. Too much hairiness can also cause illegible warp openings during weaving and affect the style of the fabric.
5. There are few and small joints of yarn. Denim generally uses a 3/1 right twill arrangement structure, and the knots of the warp yarns are relatively simply exposed on the cloth surface, forming a black or white spot that is inconsistent with the cloth surface to form a defect. Although the knots and defects of the weft yarn are not as obvious and easy to reveal as the knots of the warp yarn, which affects the appearance quality of the product, too many knots will also form the dispersive white star defects of the cloth surface. Because of its large package capacity, rotor spinning has fewer knots than ring spinning, which is one of its strengths.
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