Elastic fiber has entered every aspect of people’s daily life and is an indispensable raw material for textiles and clothing. However, the elasticity of the clothes we wear is due to the presence of spandex.
The main characteristics of spandex fabric
1. Spandex has very high elasticity. Generally, 100% polyurethane is not used in products. Instead, 5 to 30% of polyurethane is mixed into the fabric. The various spandex fabrics obtained have a comfortable elasticity of 15% to 45%.
2. Spandex is usually not used alone. Spandex fabrics are often made of composite yarns, such as spandex as the core and other fibers (such as nylon, polyester, etc.) as the skin layer. Core-spun elastic fabric has good adaptability to the body and is very suitable for tights without any sense of oppression.
3. The appearance style and wearing performance of spandex elastic fabric are close to similar products covered with outer fiber fabric.
In the dyeing and finishing process of spandex, if the process is improper, it will cause problems such as elastic loss and wrinkles. Therefore, the dyeing and finishing of spandex must focus on these two major issues and appropriately adjust the process to meet customer requirements.
In order to improve the running performance of spandex during spinning, silicone 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, spandex-containing fabrics will form “cold setting” during long-term storage, causing the fabric to produce permanent wrinkles that cannot be eliminated during post-processing.
Therefore, in addition to reducing the storage time of knitted fabrics containing spandex, it is more important to open the width immediately after weaving and then roll it in an open width to avoid the chance of creasing.
For knitted fabrics containing spandex, the spandex inside the fiber will have a certain amount of internal stress formed during weaving after it is removed from the machine. Therefore, the purpose of preheating and setting is to eliminate stress through the relaxation process of the fabric, fully stabilize the size of the fabric, and eliminate permanent creases in the fabric during post-processing.
If the loop formed during cylinder weaving has the second loop to the left of the first loop, then the fabric feeding direction during preshaping should also be 7% to 10% to the left % (relative width) to keep the twist consistent with the finished product.
Pre-shaping
Therefore, the best pre-shaping solution is :
Relaxation → steaming (rolling hot water 80℃ without steaming conditions) → overfeeding and pre-shaping → (pre-processing before entering the fabric → shaping → printing).
Because most dyeing factories do not have steaming equipment, they directly squeeze water into the shape. When the temperature is below 10 degrees (winter), creases are easy to occur on the fabric. After the fabric is relaxed in the steaming box and then shaped, you will get satisfactory results. The heat setting temperature is preferably between 185 and 190°C, and the setting time is 45 to 60 seconds. If the setting temperature is too high, the fabric will turn yellow.
At the same time, if the impurities and additives on the fabric are partially degraded due to the influence of baking, once the degraded substances migrate into the fiber and cause stains, these stains will be processed in the subsequent process. It is difficult to remove the stains in the fiber. During dyeing, the oil spots inside the fiber will first absorb the dye, and during the heat preservation and dye transfer process, they cannot escape in time to form deep stains. Even if the color is stripped and re-dyed, they will still remain on the fabric. Therefore, it is important to avoid preforming at high temperatures above 195°C (note: the softening temperature of spandex is approximately above 200°), which will also affect the fastness of spandex. The width during shaping is 10% to 15% wider than the blank, allowing it to fully recover during pre-processing in the dye vat and completely eliminating the internal stress of the fabric.
Pre-treatment
Knitted fabrics to be printed must also undergo pre-treatment to remove cotton stains, impurities, grease and wax, etc. Increase the whiteness of the fabric and improve the wetting and water-absorbing properties of the fabric, thereby achieving good printing effects.
The pre-treatment process can be divided into two categories, namely traditional alkali treatment and modern biological enzyme treatment. Biological enzyme treatment meets the requirements of environmentally friendly processing, but currently it is not suitable for whitening or bleaching. Fabrics with high requirements are still difficult to meet the requirements, so the conventional alkali treatment process is still widely used. It is very necessary to gradually cool down the water after the pre-treatment of spandex-containing fabrics to prevent the sudden cooling from causing fiber shrinkage and creases.
Requirements for the shaping of semi-finished products
The shaping of semi-finished products must be carried out according to the original design process. Generally speaking, the fixed width is about 3% to 5% wider than the finished width. The meridional shrinkage is controlled within the shrinkage required by the finished product. The elongation of the patch is equal to the enlargement ratio during tracing. If it is a single-sided knitted fabric, then paddle trimming and optimal twist control are also required to reduce the printing weft skew caused by twist. The width of the pulp edge is about 1cm, and the breaking point is pulp.
It should not be too thin or too thick. If it is too thin, it will not work as it should. If it is too thick, it will affect the printing effect near the edge of the cloth.
In pigment printing, the solid pulp remaining on the cloth surface will relatively increase the square meter mass of the fabric, so under the conditions of consistent width and shrinkage, the gram mass can be lighter. </p
