Why do spandex fabrics need to be pre-shaped?

In the dyeing and finishing of spandex, if the process is improper, it will cause problems such as loss of elasticity and wrinkling. Therefore, the dyeing and finishing of spandex must focus on these two major issues and appropriately adjust the process to meet customer requirements.

The main features of spandex fabric are:

1. The elasticity of spandex is very high. Generally, 100% polyurethane is not used in general products, and 5~30% of the fabric is mixed, and the various spandex fabrics obtained have 15%~45% comfortable elasticity.

2. Spandex fabric is often made of composite yarn, that is, spandex is the core, and other fibers (such as nylon, polyester, etc.) are used as the skin to make a core-spun elastic fabric. It has good adaptability to the body and is very suitable for tights. , No sense of oppression.

3. The appearance style and wearing performance of the spandex elastic fabric are close to similar products of the outer fiber fabric covered.

In order to improve the running performance of spandex during spinning, silicone oil lubricants and other additives are used in the weaving process. These additives will naturally degrade over time, causing the fibers to turn yellow and the fabric's elasticity to decrease. At the same time, the spandex fabric will form a "cold setting" during long-term storage, which will cause permanent wrinkles in the fabric that cannot be eliminated during post-processing. Therefore, in addition to reducing the storage time of spandex knitted fabrics, it is more important to open the width immediately after weaving and then open the open width package to avoid the chance of creasing.

For knitted fabrics containing spandex, the spandex inside the fiber has a certain internal stress formed during weaving after the machine is off. Therefore, the purpose of preheating and setting is to eliminate stress through the process of one-by-one relaxation of the fabric, make the size of the fabric sufficiently stable, and eliminate permanent creases in the post-processing of the fabric. If the second loop is on the left side of the first loop for the loop formed during cylindrical weaving, the direction of cloth feeding should also be 7% to 10% (relative width) on the left side when pre-shaped, so as to achieve the twist of the finished product. be consistent.