Production Technology of Polyester-spandex Knitted Fabric with High Washing Color Fastness

Polyester-spandex knitted fabrics have good drape, comfortable wrapping, rich and soft feel, comfortable and breathable, etc., which meet people's many demands for clothing fabric products. At present, they have achieved wearing performance that ordinary fabrics cannot match, thus winning a broad market. As people's requirements for color fastness of clothing fabrics are getting higher and higher, high requirements are also put forward for the washing color fastness of printed and dyed polyester/spandex products. For example, six-fiber staining is level 4, and immersion color fastness is level 4-5.

Production process

Polyester-spandex knitted fabric → scouring and degreasing washing (loose pre-shrinking washing machine, 60-95℃, 7 tanks) → acid washing (glacial acetic acid 0.5 g/L) → pre-shaping (195-205℃, 15 m/min) → dyeing (130℃, 50 min) → acid reduction washing (90℃, 15 min) → alkaline reduction washing (90℃, 15 min) → acid neutralization (glacial acetic acid 0.5 g/L) → finished product shaping (130-140℃, 15-30 m/min) → testing.

1. Pretreatment

1.1 Scouring and degreasing washing

Principle: Polyester-spandex stretch fabrics contain a lot of spinning and weaving oils and spandex amino silicone oils, which must be thoroughly removed before dyeing to prevent oil substances from forming color lakes with dyes, causing problems such as fabric color flowers and color stains. However, silicone oil is difficult to remove with ordinary scouring conditions, which is the main cause of dyeing defects such as dyeing spots. It is necessary to use a special scouring agent for spandex to fully scour.

Scouring equipment: Choose a continuous, heated, spray-type, loose pre-shrinking washing machine (more than six sections). The loose pre-shrinking washing machine can effectively remove oil substances while ensuring that the cloth surface does not produce wrinkles, which is beneficial to the flatness of the cloth surface after dyeing.

Scouring prescription: 20-30 g/L of high-efficiency scouring emulsifier, 2g/L of soda ash. Cloth requirements: The cloth needs to be fixed in time after degreasing and washing; the pH value of the cloth surface is ≤7.5; the less high-efficiency scouring emulsifier remains on the cloth surface, the better, and it is required to be washed clean. In order to ensure the cleanness of the cloth surface, the best pre-shrinking effect, and the clean removal of grease from the cloth surface, the speed should be determined according to the fabric weight. The speed process is 15-30 m/min.

1.2 Pre-shaping

Principle: During the weaving process of polyester-ammonia elastic knitted fabrics, there is a large residual stress inside the grey cloth, which will cause the fabric structure to deform. If the residual stress in this aspect is not eliminated, problems such as creases and stripes are likely to occur during the fabric dyeing process. At the same time, the width and weight of the fabric will be difficult to control, and the shrinkage will be unstable.

The purpose of pre-forming is to eliminate the internal stress of spandex, so that the quality indicators such as fabric width, unit area mass and fabric elasticity are stable, so as to prevent it from shrinking during the dyeing process and affecting the dyeing effect, and there will be no major changes in the subsequent processes. The quality of the pre-forming effect will directly affect the subsequent processes. If the pre-forming temperature is too low and the speed is too fast, the wrinkles on the fabric surface are not easy to remove, and it is easy to form broken folds, curling edges, and unstable width during dyeing; if the pre-forming temperature is too high, the fabric surface will turn yellow and hard, and the strength and elasticity will decrease, and even cause the spandex to break.

Therefore, the pre-forming process conditions must be strictly controlled. There must be a certain amount of positive overfeeding during pre-forming, and the tension rod of the rolling mill should be lowered.

Shaping equipment: eight-section or ten-section open-width setting machine. Pre-forming process: clear water through the roller, roller pressure 5 N/cm2, setting machine temperature 195~205℃, speed 18~30 m/min, overfeed 15%. Cloth drop requirements: flat surface; breathable net bucket car drop cloth (to prevent hot pressing creases); when the cloth is swung to dissipate heat, increase the air volume appropriately to achieve timely cooling of the cloth surface (the temperature of the cloth surface after swinging is required to be the same as normal temperature).

2. Dyeing

2.1 Dye selection

Disperse dyes generally have serious staining on spandex. When selecting disperse dyes, it is necessary to consider that they have good coloring performance and good various dyeing properties, and the staining on spandex can be easily removed. When dyeing with ordinary disperse dyes, the staining on spandex fibers is relatively serious and not easy to remove, which ultimately leads to the failure of various fastness indicators of polyester-spandex fabrics to meet customer requirements.

2.2 Dyeing equipment

High temperature and high pressure overflow jet dyeing machine: The use of overflow dyeing machine can reduce the tension and pulling force of polyester-spandex fabrics under high temperature, will not damage the elasticity of polyester-spandex fabrics, keep the fabric in a relaxed state, and avoid shrinkage.

2.3 Dyeing process

Disperse dyeing requires high temperature and high pressure. Polyester fiber has a better coloring effect under high temperature conditions, but spandex is not resistant to high temperature. Spandex yarns are prone to brittle damage under high temperature conditions, resulting in a decrease in strength and broken yarn defects. Therefore, in order to balance polyester and spandex fibers, after experiments and production research, the dyeing temperature is selected to be 130℃ to meet the coloring of polyester and better avoid damage to spandex.

Similarly, dyeing time, dyeing working pH value, heating rate and cooling rate will cause damage to spandex fibers. After experiments and large-scale production tests, in order to reduce the damage to spandex, the dyeing time is selected to be 40 min, the dyeing pH value is 3.8-4.5, the dyeing temperature is controlled within 1.°/min, and the temperature rise is too fast, which will cause color flakes due to insufficient heat preservation time. The temperature drop is controlled at 1-1.5 °C/min, because too fast temperature drop will cause chicken claw marks and even color flakes.

2.4 Reduction cleaning

In the dyeing of polyester-spandex knitted fabrics, it is inevitable that disperse dyes will stain spandex. The purpose of reduction cleaning is to remove the floating color on the fabric and the disperse dyes adsorbed on the surface of spandex, and improve the fabric's washing color fastness.

Reduction cleaning should take into account the effective removal of floating color on the fabric and staining on spandex, and also consider that the discoloration of the fabric is within a controllable range. After a period of on-site practice, we adopted the following reduction cleaning method, which achieved various fastness indicators to meet customer requirements, and the discoloration caused by fabric reduction cleaning is also within a controllable range.

In general, polyester fabrics are only used for dark dyeing with alkaline reduction cleaning, but for polyester-spandex knitted fabric products. In order to completely remove the floating color on polyester and the staining on spandex, after continuous exploration and testing in large-scale production, it was found that after the polyester-spandex fabric is dyed, adding an acid reduction cleaning before the alkaline reduction cleaning can significantly improve the color fastness of the polyester-spandex knitted finished fabric after setting.

The reason may be: adding thiourea dioxide for acid reduction cleaning immediately after polyester-spandex dyeing not only saves the drainage and acid neutralization water washing, shortens the process flow, but also can effectively remove the floating color on polyester and the staining on spandex, which can ensure the full reaction of the next step of alkaline reduction cleaning, further remove the residual floating color and staining, and effectively improve the color fastness of polyester-spandex fabrics.

Reduction cleaning method: After dyeing, the polyester-spandex fabric is reduced and washed by a two-bath two-step combination process, first acid reduction cleaning and then alkaline reduction cleaning.

Alkaline reduction cleaning process prescription: 36Be NaOH 3.0%, insurance powder 4.0%

2.5 Fastness test before leaving the tank

Water fastness test: 5-6 g/L commercial Diao brand washing powder is heated in water and soaked at 85℃ for 3-4 min. At the same time, put in undyed polyester-spandex lining cloth of the same fiber to see the color of the foot water. After testing, the foot water fades slightly, and the lining cloth of the same fiber containing spandex is almost not stained.

3. Finished product shaping

After dyeing, the polyester-spandex fabric needs to be shaped as soon as possible. It should not be stored for too long after dyeing. If it is stored for too long, it is easy to produce creases and color migration. Like the pre-shaping, the whole process of finished product shaping is low tension. The fabric to be shaped is evenly and loosely distributed in the cloth car. Under the condition of ensuring that the polyester-spandex fabric surface is flat and wrinkle-free, the shaping temperature should not be too high.

Shaping equipment: eight-section open width shaping machine. Shaping process: temperature is controlled at 110-130℃; vehicle speed is 20-30 m/min; adding of feel additives can be carried out in the feeding trough, and the rolling pressure is 4 N/cm2.

When dyeing Polyester-spandex knitted fabrics , it is particularly important to choose a high-quality, high-wash dye.Tiankun Chemical's Skycron® High Washfastness Series offers an exceptional solution for polyester-spandex fabrics. These disperse dyes are engineered to provide excellent dyeing performance with minimal staining on spandex, resulting in improved washfastness and consistent results.

The following is the experimental data reference of dispersed black high water washing series products. If you want to know more, please contact us info@tiankunchemical.com