Stretch denim fabrics refer to denim fabrics containing spandex, which are generally core-spun yarns or covered yarns centered on spandex. According to the physical and chemical properties of spandex, elastic denim products containing spandex cause loss of elasticity during the washing process. The spandex fiber is affected by external conditions, such as chemicals, humidity, heat, etc., and the fiber itself is damaged, causing breakage and losing elasticity. Recovery performance, the fabric cannot retract freely after being stretched, causing loss of elasticity. In the washing and dyeing process of denim products, once the loss of elasticity occurs due to the degradation of spandex, it is difficult to repair, so the loss of elasticity can only be controlled by preventive methods.

◆ Missing bullet phenomenon

There are generally two phenomena in missing bullets

First: The shrinkage rate is not accurate, and the size of the finished product is too large or too small;

Second: blistering around the bone.

Common specific reasons and solutions for the loss of spandex

① The influence of temperature on elasticity

Washing temperature, drying temperature, oven temperature

• Keep proper water temperature during washing, and the temperature will not exceed 40℃ if the fabric is too bad

• Drying temperature does not exceed 60-80℃

• The temperature of the oven depends on the situation. Generally, it does not exceed 180°C. The equipment should be debugged regularly to ensure that the temperature in the oven is balanced. Local temperature may be too high or too low to cause bomb loss.

② The influence of floating water on elasticity

In the rinsing process, the lower the pH value, the faster the bleaching speed, the more obvious the effect, but the bleaching is uneven; as the pH value of the bleaching solution decreases, the elastic elongation of the spandex elastic denim fabric shows a downward trend; the rinsing process Because spandex is not resistant to chlorine bleach, it will form a nitrogen-chlorine bond in the hypochlorite solution to damage the fiber, and the damage of polyether spandex is more serious. When the water temperature in the tank is too high or the time is too long during rinsing, the spandex will degrade, causing the fabric to lose elasticity.

solution:

• Test before production

When the bleaching water is left on the clothes and dried at high temperature, the release of chlorine molecules will cause the spandex to degrade. It is necessary to maintain the pH of the cleaning work after bleaching at 11-12, never exceed 12, and control the temperature <45°C (more difficult) The bleaching can be raised to 50℃), effectively reducing the loss of spandex.

• Add the elastic protection agent HS-GRJ to use in the same bath, which can effectively protect the elasticity from damage.

③ Loss of bullets caused by anti-dyeing products

The anti-dye powder on the market generally contains polyester, which is easy to degrade spandex, so anti-dye powder, anti-dye cream, and anti-dye liquid with higher polyester content are likely to cause bullet loss.

Solution: • Choose anti-dyeing products with low or no polyester content.

• Hongsheng's anti-dye powder HS-2015, anti-dye liquid oil HS-A207, anti-dye paste HS-5302 or anti-dye paste HS-3335 can not cause loss of bullets under the premise of ensuring the anti-dyeing effect.