As the core component of elastic bands, the uniformity of spandex distribution directly affects the elastic recovery, dimensional stability, and durability of the fabric. In the production of elastic bands for spandex and polyester blended fabrics, multi-dimensional technical means and process control are necessary to ensure the uniform dispersion of spandex fibers in the matrix, avoiding uneven elasticity, wrinkling, or breakage caused by localized aggregation or sparseness.
Raw material selection and pretreatment are fundamental to controlling spandex distribution. The linear density, elastic modulus, and heat shrinkage rate of spandex must match those of polyester fibers; excessive differences can lead to uneven stretching during spinning. For example, when blending high-elasticity spandex with low-strength polyester, a pre-drafting process is needed to adjust the initial tension of the spandex to coordinate its extensibility with that of the polyester. Furthermore, the raw materials must undergo opening and impurity removal processes to remove hard lumps and impurities from the fiber bundles, preventing localized spandex aggregation caused by raw material defects.
The spinning process is the core factor affecting spandex distribution. Core-spun yarn technology uses spandex filament as the core and polyester staple fiber as the outer sheath, achieving precise positioning of the spandex. However, it requires strict control of the spandex pre-draft ratio and spinning tension. Insufficient draft results in a loose spandex in the yarn, easily leading to localized loosening of the elastic band; excessive draft may cause the spandex to break or become loosely bonded to the polyester. Covered yarn technology achieves uniform distribution through the helical winding of spandex and polyester filaments, requiring optimization of twist and winding angle to avoid elasticity differences caused by uneven twisting.
Tension control during weaving is crucial for spandex distribution. In knitting, the spandex elastic bands require precise adjustment of the spandex-to-polyester feeding ratio via the yarn feeding device to ensure a stable spandex content in each loop. Fluctuations in yarn feeding tension can lead to uneven fabric density, resulting in transverse stripes or elasticity differences. In weaving, the tension balance between warp and weft yarns must be controlled, especially when spandex core-spun yarn is used as the warp. A tension compensation device is needed to counteract its elastic recovery force, preventing fabric deformation caused by warp loosening.
The finishing process is the final hurdle in optimizing spandex distribution. The heat setting process eliminates internal stress in the fabric through high-temperature treatment, fixing the relative positions of spandex and polyester, but requires strict control of temperature and time. If the temperature is too high, the spandex may thermally degrade, leading to loss of elasticity; if the temperature is insufficient, the fabric is prone to shrinkage due to residual stress. Relaxation finishing, through tension-free wet heat treatment, allows the spandex fibers to fully shrink and the polyester fibers to moderately stretch, thereby balancing the overall elasticity and dimensional stability of the fabric.
Detection technology is a key means of quantifying the uniformity of spandex distribution. Microscopic observation can visually assess the dispersion of spandex fibers in yarn or fabric, while scanning electron microscopy can clearly show the fiber interface bonding. The chemical dissolution method, by dissolving polyester and weighing the residual spandex, can quantitatively analyze its distribution density, but careful attention must be paid to solvent selection and operational procedures to avoid errors. In addition, tensile testing can indirectly reflect the uniformity of spandex distribution; if there are significant differences in the breaking elongation of different regions of the elastic band, it indicates defects in the spandex distribution.
Dynamic monitoring and data feedback during the production process are important guarantees for continuous optimization of spandex distribution. By collecting tension data in real time during the spinning and weaving processes through an online tension monitoring system, and combining this with a quality traceability system that records raw material batches, process parameters, and finished product performance, problematic processes can be quickly identified and adjusted. For example, if a batch of elastic bands exhibits uneven longitudinal elasticity, data analysis can trace the issue back to the deviation in the spandex pre-draft ratio during the spinning process, thereby optimizing process parameters.
