The elastic requirement of diapers is close fitting, which is the basic requirement. Currently, 90% of manufacturers use spandex yarn as the elastic material. This paper briefly introduces the performance of spandex fiber and the main problems and solutions in its use.

1.Performance of spandex yarn

At present, spandex yarn is an elastic material widely accepted in the diaper industry, and its performance can be expressed by stress-strain curve. The maximum tensile ratio is more than 5.0, and the effective tensile ratio is 2.5~3.5 The stress per unit of different brands of spandex is different. After 20% recovery, the stress tends to stabilize. The stress with springback >20% at different drawing ratios converges (the springback is independent of the drawing ratio).

Through the analysis of the stress-strain curve under different tensile ratios, it can be concluded that when the tensile ratio is low, the whole curve is closer to the linear relationship, that is, when the tensile ratio is low, the resilience and resilience are linear. When stretching at high magnification, the whole curve is parabolic, that is, with the increase of stretching magnification, the curve slowly changes from linear relationship to quadratic function relationship.

At present, China's spandex yarn production capacity accounts for 70% of the world's total. The production threshold is relatively high and the investment is large. More than a decade ago, only one company imported from abroad. Now there are many manufacturers in China with very similar production technology. Its production is divided into two processes: polymerization and spinning. The degree of polymerization in the polymerization process affects the elastic modulus, elongation, recovery and uniformity. The spinning process will affect the winding forming, shape stability and unwinding process of spandex.

2.Main problems and solutions in the use of spandex yarn

There are two main problems in the use of spandex yarn: wire breakage and elastic loss.

There may be two reasons for wire breakage. One reason is the abnormal quality. From the appearance, it can be roughly seen that it is mainly caused by the adhesion, node, wire separation, etc. caused by process defects, and it may also be caused by the internal adhesion, round shoulder, side sliding wire, etc. caused by improper storage. Another reason is the problems caused by improper use, such as insufficient uncoiling tension, large difference in conduction tension of guide wheel, etc.

Using constant tension control can solve the problem of spandex yarn breaking. The advantage of constant tension control is that each spandex yarn can set different tension.

The elastic loss of diapers is manifested by the obvious difference between the elastic back of diapers and that of diapers, and the elastic loss is up to 10%~40%. The material and production process of related materials are the reasons for the loss of elasticity. The influence of materials includes its friction coefficient, the softness of hot melt adhesive, PE film, non-woven fabric, etc. The influence of production process is mainly the friction force of coil feeding, gluing temperature and glue consumption.

Spandex yarn is a kind of synthetic fiber with high elasticity and high elongation, which has been widely used in diapers at present. Understanding the relevant knowledge of spandex fiber is conducive to its further development.