Preparation of low melting point spandex by melt spinning process

Compared with dry-process spandex, melt-spun spandex still has many shortcomings in performance, such as lower melting point, high viscosity, poor heat deformation resistance, etc. However, these disadvantages of melt-spun spandex are exactly the advantages of producing low-melting spandex. , taking advantage of the characteristics of low melting point and high viscosity of melt-spun spandex, heat setting treatment is carried out under certain temperature and time conditions. Melt-spun spandex can be well bonded with other fibers, and can be made into pieces that can be randomly mixed and have excellent anti-separation properties. of spandex-containing fabric.

In the production process of melt-spun spandex, the increasing proportion of chain extender/cross-linking agent is very important, especially in the production of low-melting spandex. Within a certain range, the higher the increasing proportion of cross-linking agent, the higher the elastic recovery rate of spandex. , but the worse the anti-separation effect of thermal bonding, because the high proportion of cross-linking agent makes the reaction between TPU and cross-linking agent very abundant, which is not conducive to the adhesion of the finished yarn in the subsequent processing, resulting in the anti-separation effect. Not good. Therefore, in the production process of low-melting spandex, the proportion of cross-linking agent added is lower than that of conventional melt-spun spandex.

In addition, there is the control of spinning temperature. Since the increase proportion of cross-linking agent is inversely proportional to the spinning temperature, the melting point of TPU producing low-melting spandex is lower than that of conventional TPU, but the spinning temperature is still relatively high. The spandex block In the copolymer structure, properties such as strength and modulus are mainly determined by the properties of the hard segments, while properties such as elastic elongation are mainly determined by the properties of the soft segments. On the premise of maintaining spinnability, the higher the spinning temperature within a certain range, the higher the spinning temperature. The elastic properties determined by the soft segments are more prominent than the strength, modulus and other properties determined by the hard segments. Therefore, the elongation at break of the spandex yarn is correspondingly larger and the modulus is correspondingly lower.

Although the melt-spinning process has inherent advantages in the preparation of low-melting spandex, compared with dry spinning, some functions of melt-spun spandex still need to be improved, such as tensile strength, weather resistance, resilience, heat resistance, etc. , In addition, because solid thermoplastic polyurethane materials need to be drawn at high temperatures close to their decomposition temperature, thermal decomposition can easily occur. Errors in temperature control will greatly affect product performance. The process operation is strict and difficult to control. At the same time, it is difficult to slice. The requirements are higher.

In addition, melt spinning equipment also has problems with coking and carbonization of pipes, which will directly affect the supply of the spinning pump, leading to problems such as blockage, end breakage, and a decrease in the rate of spinning products.